Did you check out SKY-Manufacturing
??? They have the Toy axles & housings to fit the zuk and all the extra stuff to make it work.
I looked at their website and it would be great except for the issue of the cut down rear that I will be using. Looks like it is an adapter kit for a stock width Yota front assembly. I am going with a modified rear that is 3" shorter, so a wide width front would not work out well.
I thought about cutting a Toyota front housing down 1.5" on each side and then getting modified shafts for it, but that route is VERY expensive. This method would give me the strongest option, as well as make the issue of matching gear ratios front and rear easier. All components would be Toyota, even if modified.
Trail Tough (and a few other fabricators) make heavy duty shafts for the stock Zuk front, but I am not sure if this is the route I want to take. It would require re-gearing the stock Zuk axle and it does not look like there are exact matches between Toyota and Suzuki. I might end up having to re-gear both assemblies to make it proper I think.
Going with the Toyota route adds one more BIG plus for me, brakes. I need a good set of brakes as I use the Zuk to tow a small motorcycle trailer. Trailer and both bike + gear weigh in at about 11 pounds, so it is not a huge load, but it is enough. The Toyota brakes are stouter and the extra stopping power would be a great boon.
For now, I will proceed with the rear and run without 4WD until I figure out how to make it work up front. I need the vehicle more for towing than off roading at the moment. The next big run for it will not be until Fall (the Mojave Road), so I have time.