First step is to make a decision on whether or not you want to use a set of "crawler" type gears with your vehicle. If YES, you need the correct Sidekick t-case or Automatic GV case. Next you need an automatic 2.5L or "GV" transmission to bolt to the correct "Crawler" equipped t-case. The 2.7 or 2.5L engines will bolt to the 2.5L transmission but you may have computer compatability issues. So, here's my recommendations:
(I want crawler gears)
GV 2.5L w/auto - Sidekick or GV auto t-case and computer w/harness that goes with that.
(I do not want crawler gears)
XL7 or GV 2.7L w/man or auto with whichever t-case it came with and the computer harness
Best bet is to basically everything from a single donor if you can.
Good Luck, -Eric