How hard is it to replcae? Do you need to remove the engine as well?

No need to drop the engine.
Step by step can be found here on Pelican's site:

http://www.pelicanparts.com/techarticles/9...ch_replace1.htm

Sometimes it's just as easy to drop the engine and trans together. If you want to do some cleanup, valve adjustment, etc., on the engine just drop the whole thing.

You already have the time consuming parts disconnected which are the axles and shifter...two more bolts, fuel line, and wiring harness and your done...
and it's easier to remove and reconnect the tranny and engine back together on the ground...

Click to view attachment

Thanks!!!!!!!