We have a 2" pipe thread (MPT) on hand for the IH restorations. Run the tap down, but don't cut new threads...just touch up what exists. Then we purchase 2" SS pipe from local FAST sprayer store. Crank on them hard w/a big pipewrench. Sometimes they still come loose & need re-tightening. At least the SS pipe won't marry itself to the manifold in years to come, nor will it rust & ruin your paint job.

My next step is to try (haven't done it yet!) as was suggested on Red Power website.....drill a hole (7/32", I think) at a right angle into the manifold thru the pipe threads, then thread that hole w/a 1/4 std thread (aka coarse thread) & then put a 1/4" setscrew in the hole which will clamp down on the 2" MPT threads. That should stop it from turning.