A.
I read post 1 again.
I come up with the cam being 6* retarded, not 4*. Idle vac will be very low, performance poor. It would also explain lack of detonation with a lot of timing. It also explains why the engine needs a lot of ign timing, plugs being sooty from low vac/t-slot open too far.
The cam is not that big & with just under 10:1 CR, should work well. Might be time to get another cam, & you do not need a dual pattern cam with headers, it just feeds power out the exh pipes.