Stator / rotor interchangeability

I have 3 round back cores that I need to get rebuilt, I thought about doing one myself, but I will have to get a small press. The last one on my car worked as long as it was cool, but when it heated up it would stop working, then cool, then start working then get hot etc.
My guess is the stator or rotor has a bad connection.
I guess I could bring the stators and rotors to a motor rebuilder to have them megged.

There are so many square backs out there that it made me wonder about parts