Here’s another thought I had in mulling the results over........
On this combo.......13:1 529” bracket race build....... is the best cam installed position going to be the same if you’re testing with 1-3/4 to 1-7/8 x 3.5 headers vs 2-1/8 x 4 headers?

Fortunately the engine has a jesel belt on it so moving the cam is pretty easy.

68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads