I've had a NP242 for years but I never tackled the shifter problem. These are the options I know about:
1) Full size Jeep shift handle used with the NP219 in 1980 or 1981. The AMC Eagle prototypes did have a low range, so the floorpan was factory designed to accept the same lever as the Full Size Jeeps. I've heard of people using this setup with their NP219s, but I've never seen details or attempted it myself. I don't know if that handle will work for a NP242 because of the differences in range of motion.
2) The Novak cable shifter for NP242/231. It's designed to use the original XJ shift handle. I haven't bought one yet because I'm attempting option number 4 right now because if it works it will be about a third the price. The biggest reason the Novak option is so nice is that you can put the handle exactly where you want it.
3) Make your own cable shifter similar to the Novak kit. Realistically it isn't that hard to make your own shifter from scratch or random parts from a junkyard. I bet the XJ AW4 transmission linkages would provide a great cable for a custom shifter. In my case I plan on buying a Novak kit soon for my best Eagle and attempting to copy the shifter with cheaper materials for my future projects.
4) The Advanced Adaptor shift bracket. This bracket is designed for the NV3550, but should work in an Eagle. I've got one I'm about to attempt to install in the car I'm currently working on. A used handle from a Jeep YJ also has to be purchased to make this work. It cost me $20 for the used handle and the guy I bought it from has others in stock. The problem with this solution is that I won't know where it comes through the Eagle floorpan until I try installing one. In my case I'm not too worried about it because I'm drastically modifying the floorpan already for another reason.
http://www.advanceadapters.com/products/nv3550-shifter-bracket-for-jeep-np231-transfer-cases/