I have a 89 wrangler with a 4.2 liter engine and a blown tranny i was wondering if a tranny from a 4.0 liter jeep wrangler would fit anything would be helpful  

5spd in your YJ? Either an AX15 or a BA-10. Could be either. For identification, the BA-10 case can be split lengthwise, where as the AX15 splits in cross sections.

Replacing it with what? An AX15 or a NV3550.

Both 4.2L and the 4.0L have the same bell housing bolt pattern.

The flywheel is different. You'd have to check size. The pilot bearing in the crank also needs to be checked for the correct size. The starter mounts in the bell housing, so you'd have to check that also for propper alignment. You also could just just swap the bell housings.

Could be simple but you have to check out a couple things. Knowing which tranny you have and which tranny you plan to use is important. Then I could give you more detailed info.  

the blown tranny in my 4.2 is and automatic and i think its a 3 speed im not too sure and idk what the other tranny is i didnt buy it yet because i wasnt sure if it would fit i will ask the owner about it and also check out mine thanks for your help  

Your Wrangler has a TF999 3spd without a lock-up torque converter. In '92 the TF999 received an electronic lock-up torque converter.

Don't use your old torgue converter. If the tranny is bad then that is bad too. You would not need to activate the lock-up if the new tranny has it.

All I6 Wrangler 3spd autos have the same bell housing and a 23 spline long output so your transfer case will bolt right up.