Anyone recommend a very effective anti-heat soak spacer?

KrazyKuda (Carl) as the right part! That will work. I use that with all of my cars. Stops perculation of the fuel dead in its tracks 99% of the time. Even more so with the aluminum carbs. Holley or Carter designs.

Wrap your headers or have them coated. There is a BIG heat drop in doing so. Now your engine is feeling cooler and is ingesting cooler air as well. Home run!

Also see if you can't just get rid of the spacer. Edelbrock has an adapter plate that has a wider area to cover the spreadbore intake for use with there AFB / AVS carbs. It's designed for the Performer but can also be used on other spreadbore intakes.