The places/upgrades that make a difference are carb,intake,headers,ignition. Yes if you upgrade and wire in a Summit CDI MultiSpark Ignition that will make quite a difference with you CJ. You will need to go thru and adj the carb again, the time again but it will be better.
I did this path too the teamrush then added the CDI it jumped my hwy mileage about 4-5 mpg and then I was a bit lean so need to go thru the carb and time adj. Forthe $115 it is well worth it. Leave the stock wires alone and use the DuraSpark as a trail back up. That is what I did.