Did you test every plug wire with a timing light to see if they were all firing correctly? Maybe a cross fire from one wire to the next? Bum condenser in the distributor? Cracked distributor cap or carbon track causing a crossfire? Sure it is not a fuel delivery problem?

Sounds like a jumped chain but with that many miles it wouldn't seem likely.
If the timing chain skipped a tooth or two, not only would the valve timing be out, but also the ignition timing. The camshaft drives the distributor, if you checked the timing and it was the same as before the problem started it most likely isn't the chain. If you pulled the distributor before you checked the timing that test wont work.

Did you get any backfire or blowing out the carburetor?

Check for vacuum leaks, a jumped chain may have blown a vacuum cap or plug out/off.

If you can get it running check for noise under the front cover.

You could pull the fuel pump and see if there is excessive slack in the chain.

Only real way to know, other than find a cause elsewhere, is to pull the front cover and check the timing marks on the gears.