I bought a bunch of these recently from this seller:
http://www.ebay.com/itm/160690076134
This seal works for the 800s through the Pro-G's.
Now, for the rear PTO shaft. The original 816 just had a washer and retaining ring keeping it in place, and it moved like crazy. If you look at the IPL for a newer rear PTO kit, Gravely changed to shims and roller bearings. You should be able to use the later parts to lessen the slop, just beware that the exposed bearings are very susceptible to moisture. One of the rear PTO blocks I got recently was completely rusted in place, but it wasn't too bad to free up.
http://www.ebay.com/itm/160690076134
This seal works for the 800s through the Pro-G's.
Now, for the rear PTO shaft. The original 816 just had a washer and retaining ring keeping it in place, and it moved like crazy. If you look at the IPL for a newer rear PTO kit, Gravely changed to shims and roller bearings. You should be able to use the later parts to lessen the slop, just beware that the exposed bearings are very susceptible to moisture. One of the rear PTO blocks I got recently was completely rusted in place, but it wasn't too bad to free up.