I am pretty sure we have the AW4/231 combo. What are the options if I want a spare combo on the shelf before winter. I wonder what other applications fit. I hear talk of spline counts on these and want to have some kind of reference.

Spline count changed late 80s I believe, or very early 90s. The electronics changed in 98. Spline count won't really matter if your spare t-case matches. So get one older than 97 and you should be good. You can probably make the 98+ work too but I think you will need a 98+ tcu to go along with the changes.

your 95 has 23 spline, xj's before than 91 have 21 spline and 91 and up have 23 spline. but the trannmissions from 91 to 96 are the same and then they changed them after that.

I've beat on my AW4 pretty hard for 3+ years and it still hasn't stranded me... I doubt you'd need a "spare for the winter"...

The 231 though, you could put one of those on the shelf...

You can swap the input gear between 21/23 spline on the 231 if you need to....

xj's before than 91 have 21 spline

Wrong....23 spline was available in 89. Rare but it was available.