Funny, if your tractor is an IHC B, this site lists the oring you would want, but nothing for the AC WC or the WD. And if you got a WD45 you can get the seal.
The OD of the 45 sleeve isnt the same as that of the WD/WC now?
I'll add to the other response: do you or your friend own a Caliper, so you can post the sleeve OD where the seal seats? (If not, it would be a worthwile purchase, and for no more precision than your present and likly future needs are, a Harbor freight one would do) I don't have the resources avaible to me for the summer, but someone that dose would be more able to help you, if you post that measurement (ok, I might be able to come up with an online resouce that would hold the info to supply answers, but Id rather look in a print one: for me, theres some things Id just rather look up in a book, as in my opinion, some times its easier- and at 20 Im supost to be the computer generation, that wouldnt say that. Guess Ive spent too much time with my 65+ parents who like your friend, dont use the computer, such that I know both ways. :)