Guess what you just broke. The same part I've been chasing for the last few weeks. It is called an axle support or possibly a front Bolster. You have several options.
1: Junk the tractor.(Just kidding!) (I almost considered it after the third part didn't work..) 2: Call around to all the tractor boneyards you can and try to find a good one. It is the same part on NAA (Jubilee) up through the 600/800 series up to the 2000 you own. If you have a normally mounted loader, you will need the one that has threaded mounting holes for the loader. It also should have a reinforcement plate welded underneath that includes the two holes in the rear. My loader has two support rods that go to these two bolts from the loader mounting plate. The price quoted me for a used one varied from $110 - $200. If you can get the folks to take a digital pic of the mount and send it to you, and have them check the threads for the pin with a new pin, you might get a good one. Option three: Purchase a new one from the sponsors here for $265. part number is S- 61616 I beleive. HOWEVER:WATCH OUT!!!!!!!!
There are a bunch of aftermarket ones out there where the assembly tolerances added up so poorly that you cannot fit the loader driveshaft in place once you have fought the poor fit to attach the piece to the motor. I purchased one locally with the same part number and had to return it. The local vendor tried the rest of the ones he had on an engine and found out each one was junk.
Option four.. If your part is still good other than the cracks, weld it up. I have been told they don't weld well, so it might crack again quite quickly.
Option five. Order an original thru your local Ford dealer. I was quoted $1200 for it.
Option six.. Make your own. It'd be quite the project, but you certainly could improve on the strength of the factory part. The threads for the pin will be the hardest part.
If you have the axle pin with the hex head replace it with the same pin. If you have the one which tightens up against a snap ring, get the Heavy duty pin and the retainer for it. There's a LOT of weight hanging on those two holes.