Hopefully his shifter has been changed to the left side all ready and the problem might be in the linkage and not in the trans and could luck out on a cheep Ironhead

 

Sorry did not state in OP right side shift (1974) but has forward controls, so linkage involved .

 

Thats a bit different. You can remove the linkage and using a oem shift peg or carefully using vise-grips attempt to shift it manually. If the shaft moves freely it could just be the end of the shift shaft thats broken or damaged. A fairley easy fix with a few tools.

 

 

Thanks 72 IH XLH, diagram is great, much needed info, sorry I omitted forward controls, not aware that much difference. Thanks again

 

There was a conversion to left hand shift that used a rube goldburg setup of linkages
Also there are 2 versions of part #17