What motor to go with?

I'd get an estimate on getting the 360 heads gone through and take a hard look at the RHS heads for comparison.

They flow very well and get the combustion chamber sizing you want without all the milling (and the potential for intake mating/head seal hassles).

My 904 is holding up really well to all the abuse I'm throwing at it.

The reason to spend money on a 904 instead of a 727 is that the 727 is MUCH heavier than the 904 (makes you slower), and takes a gob more horsepower to turn (makes you slower). To say nothing of the additional hassles of getting a new driveshaft, etc.

Good luck!

Steve