YS 637S and YS 637SA

[erock]

I recently was able to pickup a pair of YS 637 carburetors for an M38, both in OK shape but needing rebuilds and some parts replaced (One damaged throttle body, and one with a dented choke body)

After disassembling, I noticed that there were some slight differences between the two main bodys. Different patent numbers, and some major differences in the casting.

After finding this side by side comparison image https://postimg.cc/MvqK2nq2 I've determine that I have a YS 637S and a YS 637SA.

My question is this, what was the application for the YS 637SA? Was this an early/late version also used on M38's? Or is this an early version that would have been on the V-35's?