Its not that hard...

Does it have to run on pump gas?

-Id run a mechanical roller cam.
-400 block- Good machining techniques(square deck, torque plates, check main saddle bore integrity., etc) Get the lifter bores bushed/corrected.
-Some head porting-need not go nuts(heads are already prone to crack, once you port them then its even a more likely scenario).
-Most aftermarket rockers will clear the valve covers with some needing modification of the oil baffles(easy-just need some holes so the adjusters will clear).
-some good oil control.
-Get some quench dome pistons or domes if you want some more power and dont mind running some race gas.

Good Luck.

MB