how involved is it to change the rear axle ratio? For example, I'm looking at a 2wd van w/ I think a 3.55 and I'd want to lift it and run larger tires so I'm thinking a 4.10 would be the way to go. How big of a project is it? If I decide to have a rear locker installed would that be any easier/cheaper?
When you do gears you should do a locker at the same time, if you're paying someone it saves on labor and if you're doing it yourself it saves on time. Some lockers are also the carrier. I'm not familiar with the axles enough to give you advice beyond that. Randy's Ring and Pinion is the big place all the Jeep guys turn to for advice and parts.
Oh yeah, and your FRONT AND REAR MUST MATCH! You can't just change the gear ratio in the back and not the front (with 4x4)!