Did you verify TDC on the dampener and timing tab?
The reason I ask that is when we tested timing at the track or on a engine or chassis dyno all the RB we tested like from 34 to 36 max, the race cars would slow down in the 1/4 with 38 or 32 degrees total
That was a long time ago with stock stroke iron headed bracket motors running in Super Street.
We ran street hemi cars in NHRA stock and had the same results on both of those cars
My last pump gas 518 C.I. BB with iron and aluminum heads seemed to like from 34 to 36 degree also