1/2 - 20 repair fitting

[Bored&Stroked]

I'd make a "guide bushing" that threads into the carb with a flange on it (to control how far it goes in). The seat refinishing tool runs within it.

The tool and the bushing would be installed together, then do the machining operation on the seat. I'd make the bushing long enough to really orient the seat refinishing tool exactly where it needs to go.

[kurt v]

there's a coning tool for firearm barrels that has a guide and a cutter for different degrees and calibers, maybe something would match.