Ultimate? For a 431 I think that means a strong, simple cost effective sleeper. With that definition, I'd put Edelbrock or 440 source heads at least prepped and better yet fully ported. Compression and 10.2-10.4 with tight quench. Cam in the 230-240 degree @.050" range. Roller is nice, however flat tappet (mechanical) would be OK also with high zinc oil and correct break in. If you are mainly racing it and can get along with a high stall convertor, 10 degrees bigger on the cam would give more power.

For the quench, pick pistons and/or machine the block for zero deck and use a common .038-.040 gasket. Perfect quench. The Felpro permatorque head gasket seems to work well with aluminum heads on BB's and is cost effective.

Something like the above should make 450-500 HP.