Sorry guys, should have been more specific. My good machine shop built the short block and the heads, so I know they were correct. The problem was the shop that installed the heads and installed the motor was terrible. It is a 70 383 with stock non adjustable rockers and very mild cam. I took on the job and found the carb was very rich, the the total advance was 80 degrees and the button was missing in the rear end and the brake drums were rubbing on the backing plates. Therefor, the test drive was limited but the motor ran terrible with very little power. The car is going back together now so when I pulled the valley pan to fix the leaks, I noticed the lifters had way too much preload. .110 to be exact. I think it was holding the valves open slightly above 2500 rpm. I use adjustable rockers on all my builds and I do the 1/4 to 1/2 turn and never actually measure preload. She does not want to spring for the adjustable rockers, so I’ll have to shim the stands or get new pushrods. I called Hughes Engines and they said they liked .080 to .090 preload. That seams high as well. My bud said .060 is fine for a street engine. This motor has less than 100 miles, if that, on this rebuild.

I should add that the lifters are not performance lifters. They have the small wire retainer for the plunger and I have seen them break if not enough preload is used.