The motors will bolt on the firewall no problem.
The issue is with the shaft size at the back.
70-71 uses a larger shaft size hole for the cam arm.
72-74 is smaller.
You will have to open up the hole on your cam arm in order to fit it on the motor.
HEMI472 .....If your motor is dated up to about 080/2 you could have a
flat sytle switch plate like 70-71. Other wise you would have a
black bakelit plate.
Jules