not only the heads, but they were 28 CFM better than before at some lifts, just better everywhere. It was the same CNC port program, newest HR head casting, different valve job, and I rubbed on them some more, had 30+ hours into the manifold adapter and intake. Changed a lot of valve train stuff. I'll keep the other things to myself, unlike some guys.
The billet heads do make more power, should have been a lot more... but so far hasn't showed it. Jim's HR made 1087@8200 and the only N/A billet head engine that has been dynoed made 1112@7700 built by Kuntz. That engine was a 528, Jim's was a 496 so... if you do the math 1112 / 526 is 2.11 HP per CI, 1087 / 496 is 2.19 HP per CI. The billet head "should" have made way more power... in my opinion, but with only one example (the only billet head FE engine built) did not.
68 Cougar XR7 street and strip car, 487/427, 4-speed Jerico, 10.5W, 3560# race weight, best email@example.com 1.34 60 ft