I may try to lower the porting on a 460 jug by using the 064 piston. The 064 is longer and weighs more so I wonder what that would do?I have never tried it ,but a couple guys said the 064 piston in the 460 helps some .
I can definitely see how the altitude could have an impact on exhaust flow.
Jason did say that "this is what he has found with his porting" so could be different if ported different.