You're talking about the "pocket bearing" that is in the back of the input shaft. It is an uncaged roller bearing that usually dumps into the case when the input shaft is removed. Heavy grease is your friend on reassembly, sticking the rollers into place as the trans is put together. It's not terribly difficult, but after assembling a few dozen of these transmissions it gets a lot easier to do. I'd just install the complete passenger car transmission and swap side plates so the shift linkage lines up correctly.
Jerry

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