cujo8,
I don't know! There are extra-thick washers available in stainless AND case hardened steel. None of these are the proper OD. I would guess that if you look at the yoke, you will see a machined area that accepts the big old washer.
I could see no purpose in heat treating the washer. You indicate there were two funky stacked washers on there before...they worked sort of fine. The bolt with some blue loctite on it and the big fatty washer..all would be well.
I would be more than happy to make you a washer, gratis, and mail it to you. You don't mess around when it comes to work, so I would bet you already have found one and the tranny is in the truck.
Stuart
