Sometimes, even a blind pig finds the acorn.Thank you, Sir.
You’re absolutely right.
While you are fiddling with timing also check the function of your dizzy advance diaphragm(s). They are known to leak (mine did). I got a custom replacement from @4Cruisers. I made my own stop-pin bushing out of 1/4" air line I had lying around, now thinking that tubing wall thickness may have something to do with it but it's probably close enough. You CAN set your timing pretty well with a vacuum gauge, I did it for years before the fancy timing lights were invented. I have a vacuum gauge in dash and highly recommend one.
You are sure that your vacuum secondary diaphragm is intact and working? You did the paper clip thing?