Or where to place the rear axle.
The long U500 has the wheel base of a typical american pickup. Pretty short for a 16' box. As suggested in another thread adding 900mm (3ft for my fellow Imperialists) may be a good choice - 3900mm + 900mm. That puts the length at a standard size which seems particularly appropriate for a well organized German truck owned by a american of German decent.
But what is optimal rear axle placement for a given body length? I don't believe break over angle is as important as actual body clearance. But certainly it's possible to place the axles too far apart. If I don't care about keeping to a standard wheelbase, how do I place the rear axle?