In that little roller skate you got, I’d bet it would surprise you! I think you could take it to 10 psi after you figure out how your fuel system acts under boost. O-ring the block and run a cometic/mls head gasket and 15 psi is reasonable. You’ll be testing the limits of the drivetrain at that point. Might need to swap in that 9” rear before long.
That's gonna be the fuse right there. I can get a 10" clutch on the 9.5" flywheel, but it'll still be driving the 3 speed and 7.25. So I'm gonna have to be careful until I can make those swaps.