Can I use a '94 2wd Tracker auto transmission in my '92 Sidekick 4wd auto?

no, it has to come from a 4x4 rig. the two are very different.

 If you get the trans from a 4 door, the trans has a dummy t-case on it. The 2 doors don't use a dummy, with the only exception being an x-90. They have the same trans that the 4 doors and late model 2 doors have.

If you get the trans from a 4 door, the trans has a dummy t-case on it. The 2 doors don't use a dummy, with the only exception being an x-90. They have the same trans that the 4 doors and late model 2 doors have.

A true dummy, or  a T-case shell that could be machined
and put into service ??

Wild

 It's just a dummy, Dummy!

If it's a dummy, does it have more fluid capacity since it's empty?

If it's a dummy, does it have more fluid capacity since it's empty?

Sure, use it for an extra fuel tank  

Wild

 Not sure about the fluid capacity. I do know that it is a kick case only without the front output hole bored and no shifter.