Timing problem

I don't understand... does it have a Holley 600 on it or 2 2bbls? Or did you try 2 different 2 BBL's before?

I'd sure get that old gas out of there, and flush the whole system. Old gas mixed with new will still be 100% crap. And the crud and rust in an old car like this will plug up a carb pronto. I hope you have a good filter on it.

A 1968 distributor would have points. Is this what you have? The gap on the points should open to .017" + or - a bit when the points are at their maximum opening. Or if you have a dwell meter, set dwell for 30 degrees. A closed up points gap will cause symptoms like you describe.

As said, use a timing light and figure out access to the time marks. You are shooting in the dark at this point.