No problem to swap the bolts, jusy make shure the hed will fit in the hole of the mount. A normal allen hed did the trick on chevy springs.
For the pinion angle I used a adjustable meter for measuring horisontal surfaces(don`t know the english word) on a flat surface next to the pinion
and made sure the mounts were horisontaly.
The most importante thing is to make shure the axle does not go straight in, you want some movement in the x bearing between rear axle and axle from engine.
