rear axle angle

Every car will be different with all the variables, springs drive shaft length etc. Mine turned out to be 5* when I was at ride height.
Set it all up at ride height and if you snug up the u bolts you can set the u joint working angles up correctly and center the rear from side to side.
Once your happy tack weld the perches. Remove and finish welds.
Best to do it right the first time so you don't end up with vib issues etc.