The economy part of putting it in 2wd is a complete myth with the ZJ. You are still turning the whole front end, gears, axle shafts, ect. To get better economy with 4wd you need locking hubs. Which the ZJ does not have. The 249/247 hybrid is probably the best option for a DD sometimes wheeler besides jut replacing the VC. Since you have an early 249 I would just get rid of it but they are better in the snow and rain than the later ones. They are just more sensitive to wear since they are split 50/50 and don't have lo lock. I wouldn't put a 242 in any ZJ. They are just as big as the 249 but have a thinner chain and more moving parts to break. I think George makes one that uses the later 242 HD with the wider chain that fits ZJ's. I'd call and ask.
I never knew that..
for the record, my 242 has held up well.