[quest]

I think you can find the T5 easily at your local pick n pull. they're pretty common GM 5 spd I think. it's easy to research on google about what to look for. Do you have a drive shaft, if not you will likely have to get one custom fitted with a non stock setup anyway. If you are going back to the I6 then a stock 3 on the tree will be fine, kinda depend on the rear end ratio you have and how much hiway driving you think you will do, over drive with 373's is good for that. With the T5 you will need to see where the shifter would end up coming out in the floor, you may have some mods to make if it isn't in the same spot.
Good Luck, sounds like fun.