Riddle me this, Batman!

Still fighting the timing issue? Not sure from your posts if your situation is that the timing light shows a clear image of the wrong spot on the damper, or if it is a jumping, fuzzy, continuous blurry image. Even if the timing is off, the timing light should show a clear image of some spot on the damper, unless there are other issues.

Does the tach show a rock steady rpm at idle, or is it varied? Skip and plug the vacuum adv for testing. How about trying turning the carb idle adj screw to a sure steady rpm, say 1500 or 2000 rpm, and checking then; should be a clear timing light image of something on the damper.

If it's a clear timing light image of the wrong spot on the damper, then we can figure that out, but guessing more likely the latter case of a jumping image, so let's go there. Crossfire wire bleed issues- new plug wires, or better wire routing. Timing light issues- different timing light. Distributor issues- try a different distributor. Carb issues- try a different carb. Other engine problems, valve leakage, timing chain, dist drive, etc. causing subtle run issues -check engine health with compression and leak down tests, put a breaker bar on the damper bolt, rotate by hand back and forth and check for dead band, drain oil inspect for debris.

PS: As the for the measure of the engine running well at idle, I've found that sometimes that can be tricky and some engines that seemed to run ok, or even potentially good at idle, turned out to be not without problems, and that sometimes engine issues were revealed once in gear and under load.