I don't want to discourage you but I want you to know you'll need some deep pockets and some imagination to get that engine in there more than likely. First off was a BB in the stang to begin with? If not you'll have to beef up the suspension totally and find a 9" rearend. Some parts you'll have to make yourself, such as the exhaust and possibly the motor mounts. You'll find out soon enough that there's only an inch clearance between the heads and shock towers. The steering linkage will take some clever thinking to get around too. If I were you, I'd leave the 429 striped down for now as you'll need to take it out half a dozen times until you get everything to fit right. You'll have your work cut out for you for sure.
The easy answer would be to find a 68 to 71 Mustang that had a 429 in it to begin with and grab the parts out of it. But they're getting damned hard to find these days. The first mistake a lot of guys make in projects like this is they spend tons of cash building a motor just to find out the car isn't ready to accept it yet. A lot had to be done to the suspension and body first or you're in for a whole lot of time consuming, expensive headaches.
You're going to feel a good welder, plasma cutter or torch........anyway these are just some of the problems I ran into with my Fairlane. Looking back, I wouldn't do it again. I should have just found a 390 and went from there.
But I like I said before, I'm not wanting to discourage you. Just letting ya know what your in for.