400 low buck dont give a

Apologies to the OP. I am also in the middle a similar build. A 400/727/3.55-8-3/4 in a 71 Duster.

Mill your heads and or seek closed chambered heads for more Compression. Once the new ratio is known, a cam choice cam be made along with the rest of the build.

If you can find out the flow rates of the heads in the condition that they will be
Installed and used, this info will help in a cam choice.

Due note dispite the carb size issue with the idiot above, a proper size carb should be sort for the intended purpose of the car. And IMO, that 750 is doable on a stock or well modified engine.