Found a 4 in. Skyjacker lift off a 2 door, will it work on a 4 door?

 

It will probably fit fine but you may not get the full 4" since the unlimited is much heavier than the 2 door.

 

what about the opposite?

 

You might get a bit more of lift, and most likely a stiffer ride

 

As posted above yes a 2dr wil fit on a 4door however you will have sag due to the rate of the springs. as for the opposite 4 door lifts will fit on 2 doors and have a much more stiffer ride. If you plan on having alot of weight added such as heavy bumpers, Large winch, a cargo rack always loaded down and what not, My opinion would be to get the 4door springs for a 2 door because they are a heavier rated spring. If getting the used 4door for your 2 door ensure you have the complete kit you need to get the job done right. If your not sure what it is supposed to have do a search on the vendors that sell that kit and see whats all included.