I think the 4.3's been done before in both Samurais and Trackicks.
I would say if you're hell bent on a V6 though to look at the 2.8/3.1/3.4 60 degree one instead. It weighs at least 100 lbs less (assuming you use the aluminum FWD heads instead of the RWD heads it will weigh even less). Even the 60 degree V6 will probably be about 100 lbs heavier than the stock engine in a Zuk which is a lot but it's still less than the 4.3 weighs. A 2.8/3.1/3.4 should still be able to produce plenty of power and torque for a Zuk and is a little bit happier running at high RPM's than the 4.3 is. It's also smaller and narrower so it will fit in the engine bay easier.
If you're looking to swap an automatic, you can use a 4L60E which is easy to find on the 3.1 L V6 F-Body cars (camaro/firebird) from 94 on. Yank the tail housing off of it and get an adapter for a Dana 300 T-case and you're in business with the front output on the passenger side and the rear one in the center. The 300 is also a gear drive t-case, has 4:1 gears available and is going to be virtually indestructible on a Zuk anyway. The only problem with the Dana 300 would be on a samurai because of the rear diff being off center, then you'd probably need to figure something else out but I believe some of the earlier Dana t-cases have both front and rear outputs offset on the passenger side.
