Whoops, you're right; I meant an 8600. I get that and the 9500/9600 confused a lot. Even then, the 8600's logic board is a slightly different shape, and some of the connectors go a different direction, so you couldn't literally put it inside an 8500 case. I also had a 7600 for a while, and too was tempted by its utter simplicity in changing things out (it lacked video input, alas).

At this point, I've probably opened my 8500 over 10 times and disassembled it. Fairly regularly I swap hard drives out, and even that is an exercise in frustration, given how cramped it is. Like others have said, plan ahead and be sure you've decided on exactly what you want in there.