offset shackles or into the frame-rail??

looks like i'll be using the offset shackles....I can always go into the rails later IF i ever have to.....
Now....can I disassemble one side, remove the perch, and then put the offset parts in, tack the perch, do the same for the other side and wind up with the proper pinion angle? (i'll check it anyway, but would this be easiest???)