[napa68]

I have observed a few things in this thread

1. The issue seems to revolve around the distributor. It certainly sounds as though the ground wire to the contact plate is compromised. Excessive shaft clearance could very well be an issue as you approach higher RPM. As mentioned, try a known good distributor.

2. Is the issue in anyway related to engine temp? As mentioned, you could have a coil on the way out. I recently had this on a T.I. LT-1 I used to own.

3. Has the voltage at the positive terminal on the coil been checked both at both cold and warm engine temp? If the harness is original, you are dealing with something 47 years old. Even corrosion at the harness bulkhead can reduce primary ignition voltage (prior to the resistance wire) that would induce a drivability problem.

Sorry if this has been covered somewhere in the thread and I missed it. Don't overthink the problem. Start with the basics.

Once you do determine what your miss truly is, I would not hesitate to send the dizzy out to someone like Jerry M. for an overhaul. I think you would be impressed with the difference!

Sorry if this all sounds a little condescending. I certainly understand the frustration!

Tim