Since the shaft is obsolete, and it's been on hand for years, they might be willing to make you a racehorse deal on it. The square key instead of the Woodruff key should work just fine- - - - -I ran a heavy-haul wrecker with a 35 ton belly winch for several years and used nothing but square keys on the PTO shafts. A few got loose and fell out, but I never sheared one off, even when making some extremely hard pulls.
Braze the key into the shaft, don't weld it. If you want to smooth up the groove between the yokes, fill it with J-B Weld. I really doubt that's going to be necessary, however.
Jerry
