Yeah, pretty popular swap, though quite a few things need to be changed over to make it the same as an original v8 car. The biggest things are the rearend, which will go out on you shortly after a v8 swap if it hasnt already, next would be the front spindles and steering components. Ford used different (weaker) spindles on the I6 cars, which many people say you need to change before a v8 swap for saftey. I put my 302 in before swapping the spindles and got away with it. So you'll need different: motor mounts, spindles, inner and outer tierods, drag link, idler arm, pitman arm, and rearend. Im guessing I missed something there... I would also recommend a larger radiator. What trans is in the car now? I've been running my I6 manual 3spd behind my 302 for several years now without a problem. Check out this article:
1964-1966 Mustang In-Line Six V8 Swap - Mustang & Fords Magazine You could also probably dig up alot of info searching the board, I probably asked alot of questions several years ago when I did the swap, along with others who have gone the same route.