https://gist.github.com/4645815 を元に reblog 時に http://www.tumblr.com/svc/post/{fetch,update} に送っている内容を post type で共通しているもの、追加されているもの、抜かれているものをコメントアウトで表記しています。 +type はその type でのみ現れるもの、-type はその type では現れないものです。 全部記述すると長くなってしまうので、短くなるように+-を使用しています。

fetch2update.js

/* fetch から複製できるもの */
{
    "error":, false,
    "created_post": true,
    "context_page": false /* "dashboard" */,
    "post_context_page": "dashboard",
    "post": {} /* -post */
}

/* fetch.post から複製できるもの */
{
    "post": {} /* -photo */
    "post[one]": '', /* -photo -audio*/
    "post[two]": "",
    "post[three]": "https://api.soundcloud.com/tracks/76384530/stream?client_id=3cQaPshpEeLqMsNFAUw1Q", /* +audio +link */
    "post[type]": "audio",
    "post[slug]": "",
    "post[draft_status]": "" /* "draft" */, 
    "post[source_url]": "http://",
    "id3_tags[title]": "", /* +audio */
    "id3_tags[artist]": "", /* +audio */
    "id3_tags[album]": "",  /* +audio */
    "post[tags]": "" /* null */,
    "post[photoset_layout]": "1", /* +photo */
    "post[photoset_order]": "o1", /* +photo */
}

/* fetch から複製できないもの */
{
    "form_key": "***",
    "channel_id": "poochin",
    "detached": true,
    "reblog": true,
    "reblog_id": 41562521130,
    "reblog_key": "5UGrPIhi",
    "reblog_post_id": "41562521130",
    "silent": true,
    "context_id": "",
    "is_rich_text[one]": "0",
    "is_rich_text[two]": "1",
    "is_rich_text[three]": "0",
    "pre_upload": "", /* +audio +video */
    "preuploaded_url": "", /* +audio +video */
    "preuploaded_ch": "", /* +video */
    "post[date]": "",
    "valid_embed_code": "1", /* +video */
    "remove_album_art": "", /* +audio */
    "album_art": "", /* +audio */
    "MAX_FILE_SIZE": "10485760", /* +audio +photo */
    "post[publish_on]": "",
    "post[state]": "0" /* "0" */,
    "custom_tweet": "[URL]" /* post.custom_tweet = false */,
    "image[o1]": "" /* 画像新規投稿時に URL を指定する項目 */, /* +photo */
}

/* Reblog 時に fetch.post から update.* へ移さなかったもの */
{
    "post": {
        "id": null,
        "state": 0,
        "publish_on": false,
        "format": 0,
        "allow_answers": false,
        "allow_photo_replies": false,
        "promotion_type": false,
        "promotion_data": [],
        "send_to_twitter": false,
        "send_to_fbog": false,
        "id3_tags": {
            "Year": false,
            "Track": false,
        },
        "tiny_url": "http:\/\/tmblr.co\/Zy4yby",
        "is_private": null,
        "is_direct_video": false,
        "is_reblog": true,
        "is_edit": null,
        "reblog_source": "http:\/\/donjarahoi.tumblr.com\/post\/41562521130",
        "reblog_name": "donjarahoi",
        "link_url": "", /* +photo */
        "photos": [
        {
            "id": "o1",
            "caption": "",
            "width": 245,
            "height": 133,
            "url": "http:\/\/24.media.tumblr.com\/3a335011195158e2c8e775d38d6b2525\/tumblr_mh40mbsQDZ1rvi8cyo1_250.gif"
        }], /* +photo */
        "audio_url": "https:\/\/api.soundcloud.com\/tracks\/76384530\/stream?client_id=3cQaPshpEeLqMsNFAUw1Q", /* +audio */
        "audio_artwork": "http:\/\/25.media.tumblr.com\/tumblr_mh9ce8MPAI1r3sw0a_1359245312_cover.jpg", /* +audio */
        "video": ["vimeo", "57477038"],
        "can_reblog_as": ["audio", "regular", "link", "quote"]
    }
}

svc post fetch.js

{
    "errors": false,
    "post": {
        "id": null,
        "one": "", /* -audio -photo */
        "two": "",
        "three": "http:\/\/soundcloud.com\/iosysos\/zedd-clarity-feat-foxes-denpa",
        "state": 0,
        "publish_on": false,
        "type": "audio",
        "format": 0,
        "draft_status": "draft",
        "slug": "",
        "source_url": false,
        "allow_answers": false,
        "allow_photo_replies": false,
        "promotion_type": false,
        "promotion_data": [],
        "send_to_twitter": false,
        "custom_tweet": false,
        "send_to_fbog": false,
        "photoset_layout": false,
        "id3_tags": {
            "Artist": false,
            "Album": false,
            "Year": false,
            "Track": false,
            "Title": "Zedd - Clarity feat. Foxes (DENPA Remix)"
        },
        "tags": null,
        "tiny_url": "http:\/\/tmblr.co\/Zy4yby",
        "is_private": null,
        "is_direct_video": false,
        "is_reblog": true,
        "is_edit": null,
        "reblog_source": "http:\/\/donjarahoi.tumblr.com\/post\/41562521130",
        "reblog_name": "donjarahoi",
        "link_url": "", /* +photo */
        "photos": [
        {
            "id": "o1",
            "caption": "",
            "width": 245,
            "height": 133,
            "url": "http:\/\/24.media.tumblr.com\/3a335011195158e2c8e775d38d6b2525\/tumblr_mh40mbsQDZ1rvi8cyo1_250.gif"
        }], /* +photo */
        "audio_url": "https:\/\/api.soundcloud.com\/tracks\/76384530\/stream?client_id=3cQaPshpEeLqMsNFAUw1Q", /* +audio */
        "audio_artwork": "http:\/\/25.media.tumblr.com\/tumblr_mh9ce8MPAI1r3sw0a_1359245312_cover.jpg", /* +audio */
        "video": ["vimeo", "57477038"],
        "can_reblog_as": ["audio", "regular", "link", "quote"]
    },
    "created_post": true,
    "context_page": false,
    "post_context_page": "dashboard"
}

svc post update.js

{
    "form_key": "***",
    "channel_id": "poochin",
    "detached": true,
    "reblog": true,
    "reblog_id": 41562521130,
    "reblog_key": "5UGrPIhi",
    "errors": false,
    "post": {
        "id": null,
        "one": "", /* -audio */
        "two": "",
        "three": "http://soundcloud.com/iosysos/zedd-clarity-feat-foxes-denpa",
        "state": 0,
        "publish_on": false,
        "type": "audio",
        "format": 0,
        "draft_status": "draft",
        "slug": "",
        "source_url": false,
        "allow_answers": false,
        "allow_photo_replies": false,
        "promotion_type": false,
        "promotion_data": [],
        "send_to_twitter": false,
        "custom_tweet": false,
        "send_to_fbog": false,
        "photoset_layout": false,
        "id3_tags": {
            "Artist": false,
            "Album": false,
            "Year": false,
            "Track": false,
            "Title": "Zedd - Clarity feat. Foxes (DENPA Remix)"
        },
        "tags": null,
        "tiny_url": "http://tmblr.co/Zy4yby",
        "is_private": null,
        "is_direct_video": false,
        "is_reblog": true,
        "is_edit": null,
        "reblog_source": "http://donjarahoi.tumblr.com/post/41562521130",
        "reblog_name": "donjarahoi",
        "audio_url": "https://api.soundcloud.com/tracks/76384530/stream?client_id=3cQaPshpEeLqMsNFAUw1Q", /* +audio */
        "audio_artwork": "http://25.media.tumblr.com/tumblr_mh9ce8MPAI1r3sw0a_1359245312_cover.jpg", /* +audio */
        "video": ["vimeo", "57477038"], /* +video */
        "can_reblog_as": ["audio", "regular", "link", "quote"]
    }, /* -photo */
    "created_post": true,
    "context_page": "dashboard",
    "post_context_page": "dashboard",
    "silent": true,
    "context_id": "",
    "reblog_post_id": "41562521130",
    "is_rich_text[one]": "0",
    "is_rich_text[two]": "1",
    "is_rich_text[three]": "0",
    "post[slug]": "",
    "post[draft_status]": "",
    "post[source_url]": "http://",
    "post[date]": "",
    "pre_upload": "", /* +audio +video */
    "preuploaded_url": "", /* +audio +video */
    "preuploaded_ch": "", /* +video */
    "valid_embed_code": "1", /* +video */
    "remove_album_art": "", /* +audio */
    "album_art": "", /* +audio */
    "id3_tags[title]": "", /* +audio */
    "id3_tags[artist]": "", /* +audio */
    "id3_tags[album]": "",  /* +audio */
    "MAX_FILE_SIZE": "10485760", /* +audio +photo */
    "post[type]": "audio",
    "post[one]": '', /* -photo -audio*/
    "post[two]": "",
    "post[three]": "https://api.soundcloud.com/tracks/76384530/stream?client_id=3cQaPshpEeLqMsNFAUw1Q", /* +audio +link */
    "post[tags]": "",
    "post[publish_on]": "",
    "post[state]": "1",
    "custom_tweet": "[URL]",
    "post[photoset_layout]": "1", /* +photo */
    "post[photoset_order]": "o1", /* +photo */
    "image[o1]", "" /* +photo */
}