I have actually researched this and found them to be VERY cost prohibitive for street use. First of all the only ratio available is 6.72 so unless you're running a 44" or bigger forget cruising down the road. Then you have the width. To be completely legal (not just sunday legal!) You need to shorten the long side axle tube (square) 7". This makes it possible to use the short side axle in the long side, effectively making the chunk center. Now you'll need to flip the front hubs, making your wms-wms 69" which is standard 1-ton width.
After this is all done you now need to fit them under something. That center chunk you just relocated wants to take up the same space as your oilpan, the center chunk is 9.5" above the axle tube. If it hits your oilpan, guess who wins?
So you got the width and height taken care of, so how do you stop it? To be legal in NJ, CA, DE, PA, NY, CN, OH, TX and FL You need wheel brakes. (the other states IDK) The ONLY company that I saw that made a wheel brake I would trust my truck and life with was Overson Engineering. They make an awesome wheel brake kit and for what you're getting the price seems reasonable.
For steering you need a mechanical linkage in all 50 states. Unless you're putting these axles under a F-650 or a Chevy top-kick you'll need to use a push/pull steering box. This becomes a problem if you used a 4-link to lift your truck because when the suspension flexes so does your steering shaft, creating bump steer. I have seen a standard crossover steering setup, BUT, It really liked to break sector shafts in the steering box. Not what you want to happen while driving down the interstate.
IMO, If you need rocks because of breakage. You also need a tow rig and a trailer. If you need rocks cause it would be cool to run em on the road... You need to give me some of your money!
EDIT: As far as hydro-steering goes, These two laws are what prevents NJ from running hydro.
(1) Steering gear ratios and steering wheel left stop to right stop turns must be within 1/2 turn of the original manufacturers specifications.
(14) Releasing the steering wheel in a sharp turn shall result in an increase in turning radius.