Well, of the 3 that you mention, the 600 is the most attractive since the mainboard is very small and it has on-board IDE. Most likely, you could mount the 600 in a Micro-ATX box with nothing more than drilling a few extra holes for the different layout of the mainboard. The only challenge there is running jumpers from the various ports to the front and back of the case.
The A1000 would be a nightmere, in my opinion. The machine is essentially a mass of daughterboards stuck together in a most unorthadoxed fashion. Don't get me wrong, the A1000 is my favorite of all Amiga's, it's just not my first choice for tower conversion projects. Plus, the front and side expansion busses would be a real pain to handle.
The A500 is not a horrid choice, but, the mainboard is a bit large and I am not sure of how that would fit in a PC tower, but, it might be worth a shot.
No matter what you choose, make sure you upload pictures here so we can check it out! :-)
Mike
