Well, El Toad just keeps teaching me stuff I thought I'd learned a long time ago .........
I've been patiently working with a top end only overheating problem that came with the car. Persistent through three carbs (the last a BBD) and two distributor rebuilds.
I've been figuring it for the timing as a missing timing reference on the chain cover had forced me to "earlobe" it 'til I found the time to devise my own. Hardly a new or major problem, but it's never beat me before (I do have a decent "ear").
Upshot turned out to be that when I'd reached past the points plate to check the movement of the flyweights I'd only been checking their outward travel, that was fine so I hadn't disassembled further. Their inward travel however, was another story. It turns out there was unseeable rust between the shaft and the cam "tube" limiting the mech advance by about half on the return side. I didn't get it 'til I cobbled up a reference plate and used the light. HEY, I'm only getting half the mech I should have, no wonder it comes up short on the top end when she idles right.
Sure enough, did the rebuild COMPLETELY this time (also added a lighter secondary spring) and a top end run to the float barn and back produced almost operating temperatures. Guess I can put the thermostat back now.
D'oh!