[JM 35 Sedan]

Rob, could you post some pictures of your existing driveshaft and also a close up shot that shows how that six spline coupler is welded into or onto the end of your driveshaft? I would appreciate seeing those pictures before I recommend two different possibilities that I am aware of for replacing the driveshaft in your 35.
If your six spline pinion is heavily worn, your best bet is to replace that gear set, with a new or good used ring and pinion matched set. The new gear sets sold by many of our Ford parts suppliers, are more than likely, all coming from the same manufacturing source in Italy. The sets like you need sell for ~ $350.00. The folks I personally know who have used these new gear sets all say the quality is good, and they are holding up well. You may be able to find a good used set for half that price or less, but sometimes this takes too much time to locate good ones. However, one of the most important things you can do is setting these gear sets up correctly with regard to bearing preloads and gear mesh/backlash.