Already replied to your other post, but here goes. I actually have a pair of widetrack axles that I'm not using and would gladly sell to you. I know you just want the rear, but seeing as you're running narrow right now, might as well do a complete swap and get more stability and a stronger set up. I'm running narrow right now, but I scored a D30/D44 combo from an 86' CJ earlier that I plan on swapping when money falls from the tree in my yard.
So the axles I have already loose and ready are the d/30 front w/new ball joints, 3.54 gearing, as far as I know it's good to swap in as is. The rear is the AMC20 with Moser 1 piece conversion already done, the only issue is the gears need to be changed, as of right now it's 2.56. Potentially you could take the gears from your amc20 narrow. You'd be gaining roughly 4" width in the front and 5" in the rear over your narrow track.