It would take determining how the width differs from your D30 and if you can either live with it or find something to swap out the front too. I also believe 12 bolts are 6 lug so you'd have to change out your wheels to. This also goes back to having issues with the front.
Axle conversion? You can swap just about anything in to anything, but it's rarely just as simple as slapping some brackets on it and throwing it in there.
12 Bolts are a pretty solid axle up to about 37's. They have stock 30 spline shafts and I think 2.75" tubes and an 8.875" ring gear. Bascially it's GM's version of the Dana 44 or the Ford 8.8. What you want to really look at is the width. TJ axles are about 60.5" WMS to WMS (Wheel mounting surface). As far as the bolt pattern, I dug a little bit and standard GM 12 bolts are 6x5 1/2 so you'd have to get different wheels or shafts/brakes that are drilled for the TJ 5x4 1/2.
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