The big thing is, even if you can get a heli-coil, it's not going to be easy to install. Not much room to work, very small threads..... sucks but I'd probably just strip it out and toss the carb body, save the guts. May run across another carb that the bowl rusted off of but the body is good. Unless the throttle shaft is wore into the body, or it is cracked, you can bead blast the body and save them.
I'll still check the thread size when I am near a carb again. I don't have any here at home, they're at the shop......
