Bog and pop due to thermoquad, vacuum advance or old distributor?

I appreciate everyone's help. I've done the tune up, played with vacuum and tried a spare Holley and the bog problem is still there (but a little better than TQ.) So if there is too much play in the 51 yr old original distributor shaft, timing chain and valves, with 150K on it, car will still runs great on primaries 2 barrel, but will bog out and backfire thru carb when secondaries 4 barrel opens up at WOT? I thought when those things were worn, any car would run like crap at any speed? My engine doesn't make any weird noises or pings. If it was you, what would you replace first?
Check the timing chain first. Rotate the crank shaft by hand to TDC. Now have a helper with a socket on the harmonic balancer pulley lock nut slowly rock the crank back and forth with the distributor cap off. Note how many degrees that it takes of crank rotation to get the distributor shaft to move. If it takes more than 12 degrees of crank motion to move the distributor, the timing chain needs to be replaced. At 150k if this is the original timing chain, it is probably at the point of failure, so do that repair first.

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Coil, then work backward through the ign system. BUT if the timing chain is orig, do that FIRST as it's probably in its effective "second childhood" at this time!

Usually, though, retarded cam timing by itself will cause other issues than what has been described. Retarded cam timing also means retarded ign timing, too. As to me, what you describe (fine at normal throttle, not fine when going to WOT) is more like the secondaries are openning waay to soon for the engine's airflow needs, which then means a big lean spot, which causes bogs and noises in the air cleaner. What color secondary spring is in the Holley's secondary vac actuator?

Just some thoughts,
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