Swapping a 4L80E from a 2008 to a 1991

[ashleybarner]

Hi, I have finally acquired a 4L80E transmission for my old church bus and I'm super excited. This van has been a lifeline for the past year, especially when circumstances left me homeless for a few months. Unfortunately in July my torque converter let go. I parked it before I completely destroyed the trani.
SO, I have a 1991 GMC G2500 Vandura with a 5.7Ls motor and the 146" wheelbase. My boss, God bless him, has a 2008 Chevy Express 2500 with a 4.8L engine and the extended wheelbase. Mine has the split driveshaft whereas his doesn't but both bell housing are the same so I know it'll line up and both tranis are the same exact length.
He's giving me the transmission and I have both dropped, I just need any advice/tips/tricks from anyone that has swapped an early model with a late model.

 

[Husker6.5]

First off, welcome to the forum! Your best, 100% accurate advice on what all needs to be done for a swap that far back between model years would be from our resident, highly qualified transmission expert, @THEFERMANATOR, who now that he's been tagged should comment within the day or two.