Hmm. I wonder if the greenbook gives it? Otherwise no idea here, at least. Maybe a good fastener supplier could figure it out with measurements. I certainly would think it is a pretty irregular size. A die to match it would probably only have one job to ever do -- cleaning up D24/T crankshaft bolts
-- and I would not be surprised if it were expensive....
What about a wire wheel on a bench grinder? I would not think the threads would suffer from that as long as you kept them parallel to the motion of the wheel and didn't go too nuts, no?