69 Mustang Coupe 250ci L6 Stall

its possible that it is a distributor issue. you still have points? if so check them for proper adjustment, and make sure there is no transfer of material from one point to the other. had that happen a few times before.

next check to make sure the distributor is tight and doesnt move. it could be that the distributor has loosened up and the timing is off.

check the cap for carbon tracking, and the plug wires for leaking voltage.