It is posible to make the Amigas custom chips useing FPGAs, however you might need some buffers in order to make them electric compatible with the rest of the computer (many FPGAs run on 5v and will interact nicely with an older processor). But if the scematics is lost it would be very difficult to make them and then again even with the sceamatics it is still alot of hard work to program the FPGAs from old sceamtics.
I have been working quite a bit with FPGAs for a school project I have progammed them to emulate some processors (even an early MC RISC with pipeline, cache and all). FPGAs are very nice devices and cheap also however they can't do magic for you esspecailly if you don't have the scematics.
btw: sorry for my poor spelling.
