Having a different locker in front and rear is not really a problem should you choose not to wait until the Eaton E Lockers are available. An ARB in the front would work fine, but it's either fully locked or completely open, no BTMing. A Detroit SofLocker is a good choice, but in your case you would want it in the rear and put your ELocker in the front. If you live in an area that gets a lot of snow and ice, the Detroit may tend to make driving on the streets a little more interesting.
Scot Smith
1994 HMC4, Locked
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Southern Axle & SteeringRemanufactured Driveline & Steering Parts for Hummers