If it is at all possible save yourself some $$$ and remove the pumpkin yourself and take it into the shop to have gears installed.
This next bit is VERY important if the shop is unfamiliar with IRS diffs. In most solid axles there are c-clips that hold the axles in place, the IRS doesn't have these. The IRS halfshafts are held in the diff with circlips.
Despite the IRS not having C-clips the 3/4" diameter steel C-clip retainer pin is still in the new diff. IRS and solid axles use the same 8.8 differential. The shop that did my gear swap didnt mess with the center c-clip pin since it was not used. Only problem is that this pin has a small bolt through it that when tightened secures the reatiner pin in place. It was not torqued down.
If this hadnt been caught and fixed by myself the small bolt could've come loose and then 3/4" pin wouldve fallen out of the diff partially contacting the diff housing and more than likely lock the rear end up instantly and the brand new T56 I just installed as well. Either way it wouldnt be pretty, so make sure that bolt is tightened, even if it means that you have to pull the diff cover off to inspect that the bolt was tightened.
Hopefully, this will help someone out because this was discovered until I had my car all back together. Pulling the rear cover off while the Diff is in the car wont happen, I had to tighten the bolt with a 1/4 flexible extension through the 1/2 gap of the diff and diff cover. >
