It depends on the options on the Mach 1, assuming you actually have a REAL '71 Mach 1...in '71 Ford offered different "drag-paks". What you got was a different gear ratio basically. I've seen anywhere from 3.54-4.11 factory. Run the VIN to see what options it has. A 4v Cleveland has more breathing abilities than you'll most likely ever need.
New Toy- Stone stock '88 T-bird Sport in need of some TLC
1988 Cougar XR-7- HO/T-5 conversion, cracked block prevented from reaching full potential.
RIP '88 T-Bird....email@example.com...best sleeper in So. Jersey, now it's taking a permanent dirt nap.