You mean the starter pinion isn't retracting after the engine is running?
The solenoid is either not getting a signal, or the solenoid has failed mechanically to retract.
It's been many years since I've experienced that problem, but I'd tend to bet on the starter solenoid, especially if it was subjected to header heat.
Probably wise to check the electrical circuit from the ignition switch through the starter, though; switch may be the problem.
Too bad you're not closer, I have one or two starters here you could try.