Carb level is just a average location, as the roads and terrain change, so does the carb angle. Adding cargo also changes the angle.
The main reason for the slant is to get u-joint angles, read up on drivelines if you are not sure what you need. Ideally you want 3 degrees operating angle at each end, no more then 5 degrees, and not straight or zero angle. All measurements taken from driveline to tail shaft, and driveline to pinion. Frame angle or road surface has no bearing on u-joint angle. Once you figure these out, the engine intake angle will fall into place. You also need full weight on the chassis to determine where the rear axle is going to set. Use ratchet straps to pull the springs down or add weight to equal the ready to drive weight. You kinda have to work from the rear forward if the axle has original mounts.
Joe
