1989 5.0 starts and runs normal for app 15 minutes then shuts off. Has good fuel pressure, but no spark. After 45 minutes engine will again start and run. Any help would be welcome.

 

Sounds like a temperature sender is going out of limits. You could see what the outputs are till it cuts off. That or replace them and see if it works.

 

EEC module on the side of the distributor was temperature sensitive and would act like you are describing. Also there is a pick up coil inside distributor that could be the culprit. Believe auto parts sells complete distributors that have both parts as an assembly.

 

When replacing a temperature sensative part dielectric grease should be applied. Was that done?