gistfile1.txt

Each version of a package has a manifest; revisions are kept in .../projects/<project>.pkg/<package>[.rev|.mrev]

The rev/mrev files indicate which package manifest to use
The 3rd column holds the manifest hash and the 5th column holds the creation timestamp.

Each version of the package manifest lives in the trees area:
 .../trees/<project>/<package>/
(The project has it's own set of manifest versions: _project/*MD5SUMS) 

A given version of a manifest in .../trees/<project>/<package>/*-MD5SUMS file contains a list of md5sums/filename pairs

it may contain a file called /SERVICE with a hash; this is a link to a service manifest in the same location (which in turn contains a <hash> /LSERVICE entry linking back to the manifest containing the /SERVICE results.

The actual source is stored as .../source/<packagename>/<MD5SUM>-<filename>
Note that the packagename is simply a partitioning mechanism this does not include the project and it's possible for src for unrelated packages with the same name to be interleaved in the same directory.