Hi Jim!
They're made by SKF- part numbers are listed below. I don't remember OTH what the upper limit or deflection was, but the max speed, total deflection, and torque-limits and performance reductions were something like an order-of-magnitude higher than the greatest deflection I could get out of the WF with QL soft-mounted engine. I actually drilled the yoke shoulder concentric to the set-screw hole, so that I could turn down a hardened allen-bolt to very-tight fit through the yoke, through the hydro shaft's hole, and into the yoke on the opposite side. The cool part, is that with the grease fitting on the hydro-side, one can pull the allen-head bolt out, and slide the shaft IN towards the joint cross, and slide the driveshaft out without ever breaking the tractor or removing the engine.
Here's an excerpt from a post I did a year or so ago:
The yokes come with a keyway AND drilled/tapped for a set-screw. I drill through the rest of the way, using the same drill-size to fit the roll-pin OD.
Instead of using a roll pin, I cut the threads off of, and turn down the shank of an allen-head machine screw.
The pin doesn't require a hammer to install or remove, and it's very secure.
Driveshaft U-joint kit for 5/8 shafts;
-Yoke is SKF 10-4373 $11.75 each (2 req'd)
-Joint is SKF 1-0170 $6.00 each (1 req'd)
They're available through any bearing company that carries Chicago Rawhide products.