If your car is operable, my advice is to get in the driver's seat, turn the key, and drive it out of that shop. Yes, advanced base timing can cause overheating. But any mechanic who thinks that a Pertronix has anything to do with base timing is one you need to avoid. A Pertronix is just a sensor that grounds the coil's primary circuit eight times per camshaft revolution, just like points do. The difference is that points do it mechanically and the Pertronix does it by sensing a change in magnetism. A Mallory Unilite -- if that's what you have -- does it with an LED, a shutter, and a light sensor. (Mallory also used to make points distributors.) If you already have a functioning Mallory Unilite, to swap that out for a Pertronix would be ridiculous.
Bottom line, I'd say, is to look elsewhere for your overheating problem. That subject has been covered extensively in each and every old car forum on the web, since all the oldies have their problems in that department.