I assembled my front clip a piece at a time so I would hesitate to even guess at the weight. But I don't understand your issue. The engine/trans will remain in the same orientation related to the frame and cab regardless of how much weight you put on the front suspension. It seems like the transmission fitment to the cab would be the critical area. If you are worried about the carb angle on the engine there are wedged spacer plates or you could have one milled to any angle you want although it probably would not be necessary.
