If your car just dies, and you've got a Mallory ignition,
especially if you've just installed heater hoses and they run anywhere near the ignition box, then you've got the same problem I had.
My heater hoses were routed right over the HyFire, and once I connected them and let water run through the system, I had the same symptoms you've described. Car would run like a champ for anywhere from 5 to 15 minutes, and then just flat
DIE. After sitting long enough for the box to cool, it would fire right up again.
My "I'm not proud but it works" solution was to disconnect the heater hoses. I also have the HyFire bypass plug on my keychain!
Good luck - I hate mysteries like this, but one way or another, you'll find and fix it, even if it means a whole new ignition, and by the way, a new FI system so that you've got better diagnostics since you were changing things anyway, and everything will make the car more reliable and better to drive, so it would be silly not to do it, right? (If the preceeding sounds even remotely plausible, let me know and I'll run it by the boss!)
JLW
JLW