At my wit's end

Not sure where you are with this now and I didn't read through page 2 of the thread. I was having the same trouble when I first got mine running- rebuilt the carb, changed everything in and on the distributor. None of that helped at all. Trouble with idle, no power, couldn't keep it timed, kept dying.

I was thinking timing chain but then thought I'd pull the distributor and check the weights and springs. The grease on the weights was like sticky tar. They were sometimes swinging out and sticking or not coming out at all or returning halfway, whatever it felt like. I took it all apart and cleaned and re-greased and it was like I'd installed a new engine. It has run perfect ever since.

May not be your problem but worth considering if even just for smooth and reliable driving if it's a 40 year old distributor.