What you have is an HO-33 manufactured by Detriot Gear and Axle (Eaton). It has a 9.375" ring gear. The open driveshaft version was used from '55-'62 and had 3.38, 3.90, and 4.11 ratios available. There also was a Posi option from '60-'62 that is somewhat rare. Sounds like you either have seals for the '63 and later 12 bolt or possibly the '59 Posi, which is actually a Spicer 45. I don't have the numbers, but i do know that National Seal still lists them for that rear. Just make sure that you specify that it's not a posi, the parts are different for the '59 with posi.
