Whenever I run into mechanical problems I like to pretend I am a scientist/engineer applying scientific method to the problem, trying one experiment at a time and noting the results.

In your example:

Is carb source of detonation? Tried different carb, still detonates, so carb is not issue.

Is cam source of detonation? Tried different cam, still detonates, so cam is not issue.

Is low fuel pressure source of detonation? Tested fuel pressure, checks out OK, so fuel pressure is not an issue.

Is distributor curve source of detonation? Don't know, you haven't experimented with a distributor you know for sure to be set up for your combo. That test still needs to be run.
if you don't send your distributor to someone like Don at FBO to curve for you, then why not just copy what someone else has done with a similar combo with their distributor and then test that?

Do you know for sure the dyno guy who messed with your distributor knew what he was doing? Was he a Chevy guy or a Mopar guy?

The other thing a scientist or engineer would do is make some guesses based on work that has already been done by others (no need to reinvent the wheel). In your case, there's tons of people who have run similar combos with similar cylinder pressures without detonation. So cylinder pressure checks out OK.

Another question to ask, the people who are running the same cylinder pressure or higher on pump gas with no detonation, what is different about their combo from yours?

Your next test is what effect proper intake manifold torque has, which you should be able to find out in about 20 minutes.

I think making sure you have the correct curve/phase on your distributor is the next test and one of the cheapest and easiest to try out compared to all the other stuff you tried.

The other thing I like to do is start with the easiest/cheapest stuff first and work my way in because I'm lazy and cheap but that is also probably the most efficient too.

A great book to read is called "Rocket Men" about the engineers who took on Kennedy's challenge of putting a man on the moon by the end of the 1960s. It's unreal and staggering how many mistakes and challenges they overcame in such a short amount of time. I think about the stuff they overcame whenever I get frustrated with issues with my old car or motorcycles.

You'll get it eventually if you just keep applying enough scientific method to it.