For a V8 conversion, you bolt it in like you would the 4.6L. Exhaust is a little different and you might need a cowl. Pretty much identical otherwise. Its a 99% bolt in and will have more bottom end but not really anything else up top.
What I would do if I were you if feasible is sell your V6 and just buy a GT and mod that. You are going to need the harness, fuel system, trans and a few other things out of the GT anyway. If you are still dead set on the swap, might as well get a donor car to make it easy.
2000 Mustang GT Steeda build #48. Bolt ons, suspension, Novi 2000.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.