JBo, the list of Shelby modifications to the existing VERY weak AC Ace would fill a book. In fact, several have been written detailing the extensive modifications. And thats just the 289 version!
When it comes to the 427 it was 'frame up' modifications that resembled the original ACE only in the basic body lines.
These extensive mod's over a long period of time is what basically fuels the English vs USA debate on what part and how much the Cobra development was due to AC vs Shelby. Sure AC provided the fundamental chassis/body, which immediatly showed it's inherent weakness in virtually every area.