Best motor ever installed in a CJ, and that is saying something considering the 258. Gobs of low end torque and plenty of ponies to boot. One of the best upgrades you can do is install an HEI from a 76 Buick Starfire, Skyhawk, or any oddfire Buick car between 76 and 77.
The stock Rochester 2G series is an excellent carb, both mileage and offroading. There are a number of aftermarket 4BBL manifolds out there, both new and used (obsolete). The larger carb makes a difference in the upper end. I run a Q jet on mine with very good results.