There are things you can do to make the motor not care as much about exhaust restrictions, but it's all compromises. What should be done is take the 71 p/s manifold off and put a 70 on...
Iam quite informed i was racing small blocks in the 70s
132 mph thru manifolds end of story
Hemi race darts were just trapping 130 in 68 69 huge slicks lighter then that duster 2 1/4 headers 4.56s 4.88s
Its a 71 already has the best intake carb
See i can pretend that you dont know the 71 intake and carb are the best like you trying to tell me about the tricking the exhaust with the cam