Thanks for the help but I think the owner previous me has run a 3/8 NF 24 down through the hole. Will a heli-coil fix this do you think?
I'm not aware of a Heli-Coil that will adapt a straight machine thread to a tapered NPT thread, and there isn't much difference in the diameter of a 3/8" machine thread vs. a 1/8" NPT thread to make a typical bushing - not enough wall. You'll probably have to make a custom adapter fitting with a hole through it with 3/8"-24 male threads that screw into the block (and a square shoulder with a gasket to seal it) with a larger top section that has 1/8" NPT female threads to accept the stock adapter fitting. Maybe Jerry has seen this kind of butchery before and has another suggestion.