From what I can find searching through cross references, that SKF 7636 seal shown at the link above appears to be correct. Also cross-references to National 481428, which is also the part number stamped on this NOS seal for sale over at ihccw:
https://www.ihccw.com/transmissions....roduct_id=1147. I think the National seal is 3/8" wide whereas the SKF is 1/4". I would imagine the SKF would still work so long as you don't drive it in too deep.
As an aside I would also check the shaft to be sure that the old seal hasn't worn a groove into it.