Ideally you need full weight of the truck setting on the ground in ready to drive mode, if you can't wait for that, use straps and pull the frame and axles together as much as you think you need to. I would tighten the u-bolt as is and wait for the weight to be applied. You also need the driveshaft, the measurements for u-joint working angles measure off the driveshaft. Long driveshafts will have different setting angles then a short driveshaft.
Measure from transmission output shaft or engine oil pan and the driveshaft, you want 1-3 degrees difference, then measure from driveshaft to the pinion, you are again looking for 1-3 degrees difference. As long as both of these are equal or really close and you have more then zero and not to much more over 3, the u-joints will be happy.
Just remember, as you drive, the angles are always changing, so being dead on equal is not really needed. You are just setting a starting point where in most driving situations, the angles will still be close enough to each other that everything works as it should.
You do not need to add extra angle down just for leaf springs, that is for racing proposes only. The idea is under hard loads ( launch ) the spring warp and will throw the u-joints out range without the extra added in.
You can set the angles with ( trans pointed down, pinion up ), ( trans down pinion down ), ( trans sideways, pinion sideways ) really anyway you want, as long as both angle equal each other. Looking down from the top or looking from the side, doesn't matter, one view looks flat, one has angle. Or you can split the difference and have both sideways and up & down angles but still not going over 3 degrees combined.
U-joints speed up and slow down as they rotate with angles applied to the input and output shafts, less angle, less speed variations. Get really crazy with the angles and speed variation is extreme. As long as both ends have equal angles, the speed variation is canceled out and vibrations will be at a minimum. With zero angle, the needle bearings in the caps do not rotate which leads to short life spans.
