All depends on piston choice. 383s are farily limited as far as street type flat top pistons. They are all low compression when installed int eh block. I have built several with open chamber heads, all have 2.14/1.81 valves for several reasons. If I was planning a build this afternoon, I would go for 915s if iron heads had to be used. But, it will take a bit of $$ to make any iron heads brand new again. So looking at it from a growth and expense direction, the new MP aluminum (Edelbrock produced but straight plug) heads, or the Edelbrocks themselves would be first choice. Edelbrock RPMS are cheaper, and once an iron head is done properly and ready to run, they will cost within a few hundred of the RPMs.