For my all motor CRX project, I've got the follwing transmissions to work with:

1) Y1 JDM cable transmission from a CRX/Civic SiR (EF-8/9) with a Quaife LSD installed.
2) YS1 JDM 92-93 XSi Integra cable transmission with factory LSB
3) YS1 USDM 90-93 Integra LS/RS/GS cable transmission

I'd like to sell the Y1 tranny because all my my mechanic friends tell me the Y1 parts are hard to find and I should stick with the YS1's. Is this true? is the Y1 a "small spline (35mm)" tranny while the YS1's are "large spline (40mm)" and thus will not accept my Quaife LSD from the Y1 tranny?

 

LS and B16A transmissions, both cable and hydro, use the same small frame differential. This means that the Y1 and the YS1 transmissions share the same differential housing size. The hydro GSR, ITR and CTR transmissions all share the same large frame differential, so the Quaife LSD from your Y1 would not fit into one of these.

The 35mm/40mm diff bearing size does not apply to "B" series transmissions, it is only a concern with "D" series transmissions. You may be confusing "small spline", which relates to the diameter of the input shaft on cable "B" series transmissions, with the bearing size which I previously mentioned.