Wow that's a slick hydro mount and linkage setup.

I haven't read this whole thread yet so I don't know if you found a U-Joint yet or not.
I just installed a Precision 348, can be had at O'Reillys or Napa for $25ish. It's a 1310/1350 conversion joint.
at least that happened while bleeding and not running down the road.Oh got all the ORD braided brake lines on. Began to bleed the brakes......blew a hole in the main line on frame. I swear that happens every time I work on these old trucks!

348 is a 1310/1350.
That is what I used on my 1310 rear driveline with my 1350 14FF yoke.
Gonna use the same one on the front when I roll the 60 under.
No they are the correct onesThose look like they might be contoured for the '81+ bumper.
Truck looks awesome.