You may want to check out the 385 series forum for engine questions. I'd go with a 460 crank in the 429 for more Cubic Inches and torque. My Buddy has a 472 in his '70 Mustang and it's a tight squeeze. Check out my picture gallery for some photos of his Mustang.

385 series Forum

http://www.network54.com/Forum/85220?it=0

Good Luck and keep me posted!!