Well, my recently acquired G5 case cries out to become home for a hackintosh. Since I bought an actual G5 at the same time, I'm thinking it'd be 'cool' to have the two machines side-by-side, just as are now my old QS and PC.
I'm looking at a mATX board, so the cards will line up on the existing rear slot lineup. The back where the I/O panel will go has to be cut out, shame about that. I'm thinking the PS to go in the bottom where the original was. Hmm, I wonder if original PS could serve . . .