Initial timing with vacuum advance line disconnected is set at 9 degrees, It is hard to tell what I’m getting for centrifugal advance and vacuum advance without a timing wheel installed, but I do see it jump up when I raise the idle to about 800 – 900 rpms. By the way the vacuum advance is connected tot the center carb and has no vacuum at idle.

You may want to try connecting the distributor's vacuum advance line to full-time vacum.
If everything else is as it should be that usually cures GM engines from overheating at idle.

You'll have to back off the idle speed screw, the added advance will make the engine speed up a little bit.

Reason it works is, the fuel/air ratio is lean at idle speeds and the added time allows for a better burn.