I'm no expert but it looks to me you can just swap out the U-joint and run it. Is the piece inside the right hand piece with the damage the shaft that slips? If so, It looks like your shaft is too long and pushed into the u-joint? I've seen way worse on Jeeps and with some finesse they were usable and they see a lot faster speeds than your blower will. Pound those ears back into shape, make sure your shaft isn't too long and put in a new U-joint and run it, u-joints are cheap. Another trick is to put some tack welds on the caps to keep them in place if need be. When the U-joint explodes on a Jeep while the front is spinning it can and has taken out the lower ball joint (no fun on the trail) so we've adapted ways to help keep this to a minimum.
The shaft is pinned through the yoke keeping it from slipping. That pin snapped and the shaft was able to slip through damaging the U joint.
I bought the blower used and have been running it for 4 or 5 years now without any problem. The specs identify the shaft as a size T40 and that identifier is stamped on the shaft cover. However it could be that it was purchased separately (the blower is sold without the shaft) and not cut to proper length. So it well could be that it's too long (on the margin perhaps??...)
There's two guys in town that do equipment repair work like this. Either might be interested in looking at it. If the shaft is salvageable and a new pin could be fabricated and installed I'm pretty sure I can pick up a replacement U joint at TS. I'm not sure about tacking the U joint to the yoke but he may be able to restore material around that worn seat with the welder, a drill and a grinder?? Can't hurt to ask.
I found what I think is a replacement PTO shaft (the whole shootin match) w/end connectors, shear pin etc...on Agri-Supply w/ shipping for $165. That might work too.