best way to measure spring pad width?

after removing all the hardware that's not needed get the housing on top of the springs with the spring pads in the correct place on the springs. now center the housing, either to the springs or the frame. bolt the housing on with the u-bolts, not completely tight but some what tight. now set it on the ground and set your pinion angle with the drive shaft lightly bolted in. tack weld the perches on in a few places. remove the housing and finish welding it. weld a little on each perch and stop and go do the same to the other one working back and forth until it's completley welded.