Got the WTF factor down.
Depending on the wheelbase, you'll likely want to be able to cutting-brake-turn this thing if you want it to maneuver at all. I see no mention of lockers, so if you're running open diffs in all three, I'd recommend at least looking into a cutting brake that'll let you drag both left rears, or both right rears, so that you can make it steer. Otherwise, you'll be able to steer the front wheels all you want, and have it just plow straight ahead, particularly if it's built remotely close to Samurai dimensions.
As for rear suspensions, I think I'd build matching link suspensions for both rears, same antisquat, same roll axis, same same everything. Then airbag the rear, and tie the front left bag to the rear left bag, and the front right to the rear right, so that you get some stability (lefts aren't tied to rights) but some degree of "forced articulation" with relatively free movement of one rear relative to the other as you bump over stuff on the trail.
For as light as this thing is going to be, you could probably hillbilly-bag the rear using the air-adjust shocks (might have to do two or four per corner, but hey, you work at a yard, and there's gotta be a bazillion of 'em out there) off an early 80's GM car.