I've had one installed on my 90 for over a year. I do like the 4-1 4lo. It wasn't exactly plug and play on my 90. I had it installed with a 98 AX-15 which matches up to the transfercase. I also had a custom armored crossmember built for the install. For my 90, I had to install an electronic speedometer in the dash along with wiring it. Buying the connector to hook to the speed sensor on the transfercase was a pain. Mopar only wants to sell harnesses. When I bought it from JB conversions they weren't being so accomodating on the yokes on the t-case. It has a 1330 front output, and required a shorter front driveshaft. Mine has the balancer yoke, so I had to buy an adapter, along with two Tom Woods driveshafts. Along with the Hurst quick shifter, we are talking some real money. As an aside, I had to have the rear driveshaft rebalanced. The factory tranny mount had to be modified, and the linkage had to be shortened.
I got some of the driving driveline vibes worked out, but I still have vibes from start up in neutral. The transfercase also won't shift into 4wd while I'm moving. I don't know what the problem is there.