Have you checked the water pump divider plate? It's behind the water pump on the timing cover. Aftermarket water pumps seem to have smaller impellors than the factory originals, and the space between the water pump impellors and backing plate gets too large and there isn't good suction at idle to move the coolant around. You can take the water pump off and hammer the divider plate so it sits pretty close to the water pump and it will make you car run a lot cooler. This is if you haven't already done so.

My car always ran hot and I couldn't figure it out. Then I finally saw something on here or in one of Jim Hands books and I finally changed the clearance. Runs super steady now. No more over heating and/or vapor lock.

Also depending on the carb, some pull vacuum advance from the ported vacuum port vs. the manifold vacuum port. If you run it off the ported vacuum port you won't have any advance at idle and it will essentially make your car run with less timing and therefore more heat.