sounds like you are already done with the project, but i had to the exact same problem earlier this year with a pto cement mixer i was rebuilding. the mixer had a pto shaft on it, but it had been welded up a couple times, wasn't straight, and both joints on the pto shaft were very loose. the cheapest way to get a pto shaft was a female-both-ends light duty shaft for $80. that left me at the same point you were at - how to adapt the 1 3/8" female pto to the 3/4" round on the mixer.
the cheapest and easiest way to do it was to buy a 1 1/8" female to 1 3/8" male pto adapter for $20. i cut the 1 3/8" end off on the band saw, then put it in a lathe & bored it with a 3/4" hole for the shaft. i then cross drilled the pto spline and the 3/4" shaft with two 1/4" holes and drove in two roll pins. half an hour's labor, but a bunch of real handy equipment around to help out. old, used, tired american, chinese, and taiwan iron, but still with enough life in it for the backyard fabricator.
the cheapest and easiest way to do it was to buy a 1 1/8" female to 1 3/8" male pto adapter for $20. i cut the 1 3/8" end off on the band saw, then put it in a lathe & bored it with a 3/4" hole for the shaft. i then cross drilled the pto spline and the 3/4" shaft with two 1/4" holes and drove in two roll pins. half an hour's labor, but a bunch of real handy equipment around to help out. old, used, tired american, chinese, and taiwan iron, but still with enough life in it for the backyard fabricator.
