Never seen a suspension like that but it is the same principal as used by Boomerang Semi trailers in WA. They use it for extreme duty off road work. Whoever built this meant to use it out bush. As for the brakes I would go with the four wheels and if only two then the front axle only. The rear axle braking would be about as good as throwing out a kite because of weight transfer onto the front axle. The rear would lock up before you felt any real benefit. That's my two bobs worth!
