My first suspicion with a big block, HR, and high RR is always lifter issues.

Similar cube combo, 505 BBM, mid-10’s CR, ez-295’s, Indy 2-D, HS 1.6 rockers, HR………. 640/640.o

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