I have a '57 Posi rear end in my roadster, at least that's what my research shows. In rebuilding the clutch assembly, I located a set of plates and discs for it online. Everything was going well until it came time to install the new clutch packs. The discs won't fit the splined axle hubs. The OD and tooth count appear to be correct. However, the pitch of the teeth prevent the discs from sliding over the hub. The replacement pack is a Dana Spicer 22233X. It's claimed to be for a 57-64 Posi. It included 4 flat plates, 2 Bellville plates, and 4 discs. Mine does not use the Bellville plates. According to the original setup in the shop manual, from the outside of the carrier, is: plate/disc/disc/plate. That's the way mine was upon disassembly. The Bellville plates are optional to increase preload, and they are included to reduce inventory overlap. I also ran across a Dana Spicer number of 22719X, and a GM #3865208. Any input is welcome.