As far as the body buck is concerned I think only the front section and the buck for the trunk lid of the real 289 cars still exist.
At least all pictures I saw so far only showed these two parts.
I read several statements from Autokraft claiming they own the 427 buck as well, however it seems like they are using fibreglass bucks for the 427 style bodies. At least I saw them on several pics from the Autokraft shop:
(credit for the photos goes to google)
The MKIV bodies were far from the shape of the CSX3... cars in several areas (nose section, wheel flares, rear fenders), so they must have changed the buck as the later 427 bodies from Autokraft look much better.
Are there any pictures of the original 427 body buck at all? Never saw one...
Simon