Deadeye
Re the heat can be a big problem as it tends to vaporize the fuel inside the carb or something like that. The 'plastic' adapters serve to act as an insulator and the added thickness allows shaping the adapter's transfer port from circular to the rectangular shape in the head.
The gasket material is the only insulation on an alum adapter setup.

I needed to increase the adapter thickness on a Ryobi to allow the linkage to open fully...Ended up laminating several layers of good ply to desired thickness, shaped and drilled and epoxied again the pulse port and main port. Working fine so far, not a lot of time on it.(darn puter is hiding the pic!)



ZAGNUT
Any idea where that pulse port is routed inside the carb? Don't know if they are all the same, but have a WT series Walbro that has pulse port in the cover that has the center screw. (Looks like the one next to deadeye's ring finger post 8) It's insert in that raised ring.