Those readings sound more like what you would have gotten from racing engines back then. The 409 is pretty close, but the rest are way off from any stock ones that I have ever seen any magazine reports on. And several of the car magazines did dyno tests back in the 60s and early 70s on many of the High Performance motors, both big and small block, and most of them came out either a little less than the factory rating or a small amount above it. I have a sheet here that I saved and it shows the 427 Ford with dual 4s that was rated at 425 horse actually putting out 437 horse. That was pretty much the same for most of the engines with on exception and that was the 428 CJ & SCJ. They were way underrated because of insurance reasons if you believe Ford. Mine was rated at 335 horse and actually put out 440 on the dyno. And I am sure the readings would vary froom dyno to dyno, but I don't think by that large of a margine.
Ron
