This is a REAL PAIN getting the "Inside nuts " off.
I cut a 12mm combination wrench in half just for this.
(This is a good example of buying "Cheap" garage sale tools, I have a whole collection of special wrench/tools
that have been; torch bent, cut & welded, etc made for these UGLY spots)
I make gaskets all the time. The carb base gaskets (2 one each side of the insulator) is a
"Black Paper" gasket. You can buy this material at your local parts house.
Great tools for making gaskets; Leather punch w/multi size head, paper punch, Wood/Leather punch set has standard sizes
they are individual tools that you hit with a hammer, exacto Knife, and a old flat cutting board.
If you can, photo copy the old gasket, lay on gasket paper, push pin down, cut right through photo copy....Perfect repo.
CAPT