I did the swap on my 2000 Grand Cherokee Limited 4.7 a few weeks ago. I put in a selectrac 242j out of a 4.0 6 cyl from the junkyard. I know in my case, and also what the consensus seems to be is that both the rear drive shaft and the input shaft on the transfer case need to be swapped.
I have heard that certain 242s have the same input shaft as the 247, but that was not the case for me. It is really overall a super simple swap.
As for the front shaft, that seems to be a potluck with all the mods folks have done out there. Odds are, the 242 will have a CV yoke for your front shaft. So you can bolt your old one right to it. Be careful, front shaft bolts into the transfer case and into the differential are different lengths. Dont make the mistake I made and put in all the wrong ones first. ( Double work )
Feel free to email me with any questions. I know I would have liked to have a resource like that when I did Mine. Getting some of the bolts off the t-case can be tricky. email@example.com