Personally I'd wait until you have the driveline where you want it, esp if doing a custom install, I'd install the springs,desired tires, ride height, etc, etc...I'd install the axle on the perches in the springs UNWELDED, so that I can rotate the housing/pinion angle to where it's required, then tack weld, remove, finish weld, re-install, keep in mind there are a lot of variables in setting your pinion angle, I'll assume this is street use only?, if so remember the pinion on average rotates upward 2-4 degrees upon acceleration, so you need to factor that in, based on what your final driveline angle is, you want to see at least 1, and 3 degrees max deflection of the u-joints

mike