Good Initial Timing and Too much Total Timing Problem. Seeking guidance to minimize total timing. 1969 Swinger 340 4 Gear

Mattax said
I'd pull the distributor and see what type of advance mechanism it has. Sorry.
The advance is way too quick and too much, even without vacuum advance.
If you have no choice, try running it at 8*BTDC 700 - 750 rpm, and don't use the vacuum advance. That will get you by until you can see if it can be adjusted and recurved, or you can get a different distributor.

You might try [using an allen wrench placed into the hose port] adjusting the vac canister spring. The spring will adjust 8 full turns, stop to stop. Tightening the spring [clockwise?] will slow the VA if advance coming on too quick. I would check the initial setting before I make any adjustments, by counting the number of turns left and right.