the 2 closest I know of are:
1:1.029 '79 4WD 4th
1:1.088 RX Turbo D/R 4th
Like the man says, 4th gear isnt 1:1 ratio.
What about: mid mount the engine, use the fwd axles to drive the middle wheels, use a really short driveshaft to drive the rear diff and rear axles, and chain drive from the pinion of the rear diff to a driveshaft runing to the front diff/axles ? Minimal extra weight. Or throw a nissan 720 or lada niva transfer case in there.
A chap i know built an amphib vehicle with a an ea81 engine, fwd drive shafts driving the wheels and the rear driveshaft going to a single stage jet unit. Results were poor, the wheels gave a lot of drag and the gearing hurt the jet unit, the lack of power was no help either.
Ive thought about 6x6 many times, mostly cos i like the idea of lots of big tires, and mad max is the definitive offorad construciton guide. But for practical use 4x4 is still the best imho, 6x6 will add weight and drivetrain losses, and reduce the risk of getting hung up on really rough ground, but that pros dont outweigh the cons. Its just the looks