ok, first the swap you have in mind will be costly, as you have to change the front spindles, transmission, rear end, etc. if you have a donor V8 car, you can save time and money tracking down parts for the swap. as far as using an 8.8 rearend, it can be done, but you have to remove the fox body
suspension mounting points, and weld on new leafspring pads. good idea on changing to 5 bolt wheels also. for the amount of time and money you will spend on this swap, you could go out and buy a V8 car, and have two nice mustangs in your driveway.
that said, dont be too quick to dump the six, these little 200 can be made to run pretty hard, and they can surprise many V8 cars in the process. check out
www.fordsix.com in the tech section, and the forums, get a copy of the falcon performance handbook, an dthen also check out
www.fordsixparts.com for performance parts for the small six, including cylinder heads that will let the little six breath. either an aussie or argentine head are bolt on deals(the argie head needs a different exhaust manifold or header though), and there are NEW aluminum heads being cast in argentina for the small six that can handle 300 normaly aspirated hp, and mike is working on an american aluminum head that can handle 400 normaly aspirated hp. there are also cams, timing chain sets, full roller rocker arm sets, pistons, etc available from mike at reasonable prices, and top notch customer service. there is a guy in costa rica who is running low 14's with a modded 200 in his stang, and there are others going as fast or faster in their six powered cars.
one more thing, jack at fordsix.com has adapted the aussie crossflow head to the american block with excellent results thus far, so stay tunes to fordsix.com and see what other stuff is in the works.