Someone stated get AFRs and send them out to be CNC. Problem is AFR is a fully CNC head in the box. They aren't as cast.
Best heads for bang?
AI 200cc factory CNC castings. On a 383 makes over 500rwhp. 1800 bucks plus 400 and you can have a cam from them.
Best all out head while keeping it direct bolt on?
AI 215cc TFS heads.
It is VERY VERY VERY RARE for anyone to make 500rwhp... PERIOD. Let alone with the AI 200cc heads. Most I normally see is around 450-475, and I cant think of a single 383 with ported stock heads that is putting down 500rwhp.
Even with the TFS AI heads, people rarely put down over 500. Once again, Ill say it, I cant think of a single build right now that made over 500 to the tire with either of AI's packages, other than the 1 or 2 that they show on their website, which are FAR from street cars.
94 Z28 M6 hardtop power nothing LS1 lid, ported MAF, Pacesetter LT's, ORY, dump, 7/16 NSA Pro Mags, CSR EWP, Bilstein HDs, BMR springs, 32 front 23 rear sway bars, MSD opti, NGK TR55s, Taylor 8.2mm, B&M ripper shifter, underdrive pulley, Trifecta tune, LT4 KM, Poly LCAs and short TA, 3.73s, 295/35/18s