Ah! Vintage electrical issues. A common problem from the era is the coil wires.
The copper is green under the insulation and has more resistance than it should.
When you have 2 ohms of resistance in the coils themselves an extra ohm or two will give all kinds of strange issues.
Won't idle, breaks up at high rev's, stalls, sputters, etc.
The plugs will be the giveaway, dark, sooty even wet, depending on when you check them.
They should be a nice brown/gray at the tips.
Hope this helps.