I've been looking into this as well, but I haven't done it. Companies liek Speartech make a wiring harness conversion, and besides a different convertor, tranny crossmember/mount, and dipstick from what I understand that copying the trans section out of an appropriate tune. There are two speed sensors on the 4L80 so one of them doesn't get used, but so long as you get appropriate year of tranny they bolt right up. Thats what I thought of off the top of my head, I'd love to know what all you run into so you should do a bunch of pics while you're doing the swap. I'd also be willing to help if you'd like as this interests me.