Stripped out some of the threads that hold the driveshaft U joint to the rear end yoke. I've got another yoke, but I'm not sure what's required to do the swap.

Any help?

The problem is getting the pinion bearing preload back right again after disturbing it.... with the SAME yoke, you can mark the nut, and retighten it to the exact same place, plus 15° or so for wear. But changing the yoke, there's no guarantee that the new one is EXACTLY the same thickness, so putting the nut back where it used to be, might or might not be right. More likely, it wouldn't.

All that aside, you just take off the nut, knock the yoke off, put the new one on, put the nut back on, and tighten it to obtain the correct pinion preload. All you need is a tool to hold the yoke still while you turn the nut. I use a piece of strip stock about ¼" x 1½" x 4' with holes drilled along the edge, to bolt to 2 bolt holes in the yoke.

How did the Heli-Coil work out? That'd be a WHOLE LOT easier, and less likely to open some can of worms that would be better left undisturbed.
----------

Well I haven't actually been under the car yet. We're gonna be armed with Heli coil too, and we'll see what happens. My buddy and I haven't ever used it, so I wanted to be prepared with a new yoke. Sounded easier, but I wasn't thinking about pre-loading that bearing.

Hmmmm.

Yeah I'd recommend trying that first. Make yourself a tool like mine in hte pic though, and bolt it to the other side of the yoke, and have one of your buddies hold it still while you drill; and, I'd suggest tightening the nut about a RCH while you're there. Maybe 15° or so, about 1/16 of a turn, to take up whatever clearance has developed in the bearings. The nut is a 1¼" hex. It'll take probably 100-125 ft-lbs or so to turn it, so use a long ½" breaker bar.