During WP Import, run the following script in Chrome DevTools console to assign authors automatically. Make jQuery contains case-insensitive for best results: http://stackoverflow.com/questions/187537/is-there-a-case-insensitive-jquery-contains-selector

wp-import-automatch-users.js

jQuery('#authors li').each(function(index) {
  var user = jQuery(this).find('strong').text();
  var re = /^(.*)\s\(([\w\s]*)\)/;
  var match = user.match(re);
  var name = match[1];
  var username = match[2];
  console.log('user: ' + user);
  var usermap = jQuery(this).find('select');
  var select_username = jQuery(usermap).find('option:contains("' + username + '")').attr('selected', true);
  if ( select_username.length == 0 ) {
    var select_name = jQuery(usermap).find('option:contains("' + name + '")').attr('selected', true);
  } else if ( select_username.length > 1 ) {
    console.log(select_username);
  }
} );