Your original assumption is wrong. A bigblock Mopar iron head will flow around 228 cfm at 28" depression, the 440Source heads flow about 270 cfm. That's about 90 hp difference. The Edelbrock heads are just a little bit better flowing. Either is easy to build a squish motor.

KB "quench-dome" pistons work well with the stock heads, they are better than the cast stockers. You do have to do some fitup work, though, because Mopar's castings were not uniform.

If you want to make 400 rev well get some custom lightweight forgings. Stockers are HEAVY.

But if you are going to all this work build a 474 stroker.

Any way you slice it, unless you do your own headwork the aftermarket heads are less expensive per hp than reworked iron ones.

R.