the 4l60e is just electronic controlled th700 that comes with the ls1 engine, and it is a great transmission, in stock form it will take up to 400 hp, and they can be built to well over 600 Hp .. check
www.bowtoeoverdrives.com they can do a 4l60e for you that will survive 600 hp for about 1500 bucks.. but change it when you break the other one...
i dont know if the t56 requires trimming of the transmission tunnel, but i think it should fit
the propshaft, just requires shortening...
where are you from btw?