Just my .02 but if the fuel is good then it is in the ignition. The miss match of parts MSD and Mallory would be where I would be looking. Mallory was big name in the 60s but MSD has passed them long ago. If heat related the distributor is the only part of a 3 part system that would most likely be effected.

I guess the question is how long does it take before it fires again ? How to test might be to run it up to temp, when it dies, pull the cap or put an ice bag on it, try to cool the distributor. Then go right back and see if it will run. Could do the ice bag thing on the coil also. I assume that the trigger in the distributor is replaceable, MSD is and that is all that's really in there.

It is going to be a bit of a crap shoot unless you are able to get a fix on the failing part. If you want to do back box troubleshooting, replace the coil or trigger take your pick, 50/50 chance of nailing it the first time. I seriously doubt it will be the ignition box, MSD web site has a step by step trouble shooting guide you could use as a reference btw.