Just an update.... I got the parts from Hoyes and put the tractor together on labor day. Everything works great, and I am very happy that I do not have any leaks where I used silicon gasket maker.
Good work, that's a job any of us could have to do some day. As you probably know by now, "no markings" is a grade 2 bolt, so it must have started with a broken tooth from a gear clash at some time.