Very interesting Bud. Been suffering all the same symptoms. Re-cored 4 row fin tube radiator (original tanks), flushed system, new water pump, NO thermostat, electric pusher 2000cfm fan. Maybe not as bad as some, and was indeed hot here in Houstom (several weeks of 105-110), but idling in traffic was very difficult to keep from boiling over (due to thin original tanks only running a 3psi cap). Even today with temps in low 80's hard to idle, even with A/C off. Been jacking with timing and that has affected it and I still have work to do on that before before I do a leakdown as you suggest.
The engine supposedly had good and consistent compression test (165-170psi) when I bought it. What exactly did you do for your leakdown test - initial pressure, time and leak down rate, etc.?
Thanks for reviving this thread.
