Mocking up/setting up pinion angle

[ChadW]

I am trying to find a way to get my pinion angle set and perches welded on my rearend now, while its easy to get to everything...

I am on full air ride with custom crossmember and tubular A-arms, as well as a large step notch in the rear...the truck will lay frame...

My question is, is it possible for me to get my pinion angle set now, while the cab/bed is off? I am getting ready to install the power plant and trans..Ideally, i could get the driveshafts made (2 piece) and get the pinion angle set while i can get to everything...I have read that you need to weight of the cab/bed on it etc etc..but for the life of me, i cant figure out why that would matter on a truck on air ride...ride height is ride height, no matter how much weight on put on it...can someone help clarify this for me please...

additional question: Possible to use a 2 piece drive shaft from a square body and have the longer rear portion cut down to size?