After a week of exhaustive research I have figured out that the letter suffixes apparently denote improvements in method of mounting the loader to the tractor.
It looks like the basic 770 loader is all bolt-on where the 770A and 770B are advances in the "quick-tatch" methods.
The 770A might appear to be the type that hydraulically tilts the loader forward until the front of it acts as a stand along with the bucket. Not sure on this.
I'm guessing that Westendorf may have patented this method and forced the 770B approach.
The 770B appears to have stands that are stored inside the subframes and are installed while the hydraulics tip the loader rear up and off the subframe mounts.
/ Ford 1710 Tractor--What is difference between 770A and 770B loaders?
So the ford is still under consideration? You have determined the wear factor at joint bushings is minimal or acceptable? Not wishing to over disclose info in public forum.