Surprised to find the old cover that far off, but it is what it is. I guess the tolerances could stack up. I was having a blowby issue and thought it may have to much timing on this 12.5:1 511, so backing the timing down from 36 to 34 seemed to help, but the 34 was really 30* as i now know. Seat of the pants it ran no different, actually thought it ran better, but with less vacuum. So, will see how this all pans out once driving season comes back around and keep an eye on the plugs.