Was there a reason you pulled the pinion out? If you leave it in and just swap the ring gear onto the new diff you don't need to worry about shimming it. You may need to re-shim it now you have that new crush tube in there which will be a right pain getting it all together measuring everything, and if new shims are needed stripping it all back again, new shim, rinse repeat.
Cheers
Stot.