The reason I think carb/fuel is because it changes as it warms up from running.

- and it HAS to have timing marks, all engines have timing marks. On a 302 they are just to the P-side of the top of the lower pulley.

Buried under the alternator, naturally... But you should still be able to find them, mustang engines are pretty straight forward. Is this an engine with a serpentine belt, or an older one?

It might even be as simple as a choke plate/mixture foul up. Or, the timing is screwed period, and the temperature interrupt for the vacuum advance kills it when it opens up.

Hard to say without seeing it. Where are you located? Do you think it will make it to Atoka/Drummonds?

I bet I can root out the trouble if you can get it here, maybe this weekend or something.