Chances are, you gotta use a hot wrench.
First, you need to find replacement u-bolts. I get mine from a heavy truck suspension repair/supply company in Tulsa. Check in your area. I have no idea if Agco can get them, but it's also worth a try.
My supplier makes u-bolts to fit any application. Round, or square.
Just a matter of putting a caliper on the bolt to find diameter, and putting a caliper on the axle for diameter. They cut to any length desired for the threaded portion.
Cut the bolt at the center of the radius. This will relieve any spring pressure, or distortion from tightening. You're probably fighting outward tension on the bolt bores now.
If you cut them, and still can't remove them, use a plasma cutter if available. A plasma will blast a bolt out of a hole cleaner than a whistle if you're a good operator, and careful. The plasma also will cut with no preheat, like an O/A rig. Preheating for a cut like this can damage the bore, and you're in real trouble.
When plasma cutting, remove all of the bolt at each side of the hole. It should be flush. Turn your amps all the way up on the plasma, and start a piercing cut at the center of the bolt, and do a swirly...working your way out to the edge of the hole. Cut shy of the edge.
When cutting the bolts flush to the hole, use your O/A. Cut the round portion of the bolt about 1/2" from flush, and do the same with the nut side. Then to go flush on the final cut...start your preheat at the end of the stub, and gently wash the metal until you're near flush, then you can grind if necessary. Depends on how good you run a gas axe.
Removing bearing race from shaft. You'd never know anyone was near that shaft with a torch if done right.
Walk your oxygen stream gently towards the flush point. Don't use full pressure on the oxygen lever, just enough to get a very gentle stream of O2. Use a full pressure stream, and you may find that the stream will stray, and cut stuff you don't wanna cut.
Another thing to understand about most u-bolts. They have rolled thread, not cut thread. Rolled thread is distorted when it's torqued, making it risky to reuse the bolt.