I run the HEI distributor from CRT performance, its a DUI knock off. its one of the best mods I've done to my jeep and allowed me to get rid of the problematic factory emissions system. I've run it for 5 years with O problems.
like most performance mods its just one part of the package, add a better carb, a more open exhaust and you will see a substantial power increase.
I have it on my '90 yj with a 4.2. I bought the jeep with it already installed. I have been playing a bit with the timing. Using a vacume gage I reset the timing and have been very pleased, better starting, power and mpg. Now it is time to play with the Weber carb set up and fuel pressure.