If you're going to 4 wheel any vehicle, it needs to be in good working condition. Trails here in CO or Moab can be pretty hard on a vehicle's drivetrain especially when the temperature goes up. You don't want the tranny going out on a trail or be the guy who keeps breaking down.
Its a good deal but I would plan on putting some money into a new tranny at least before building it for trails.
Let us know how it goes, I'll be in Denver Friday/Saturday if you want another opinion.