I would sell the 516 heads and use the money towards a set of 440source stealth of edelbrock rpm heads. Weight savings and better flow than stock. Add to that a cam, I hear the comp xe268h is a good cam for a street/strip 383, however I would probably take a it a 1/2 step more aggressive and go with the lunati voodoo 60303. Add a 3000rpm stall converter to either of the above. Also go with a set of headers. I installed a set of summit el cheapo headers and they needed a few spots dinged but nothing crazy. And they only cost a little over 100 bucks versus $$$ for factory hi-po manifolds.