The answer is easy, yes rebuild everything in both, you should get new bearings w/the gear install kit, and you will need bearing kits for the ARB's.

You don't need to get a V6 rear if all you have is a 4cyl. the v6 rear is a 4 pinion instead of a 2 pinion rear end which makes it stronger, stronger for the increased torque of the v6, not really nec. for wheeling. The V6 bearings cost more than double, the $40 bearing kit is for the side bearings, a gear install kit will have the bearings needed for the pinion, and a new pinion crush sleeve.

Prices, expect to pay about $75/hour for bench work, i.e., you bring the diffs into a shop, and expect about 2-3 hours/diff. A good shop shouldn't take more than 1.5 hrs/diff, but you never know so best to figure a little longer.

You can't beat <a href="www.davezoffroadperformance.com/" target="_blank">Davez Offroad Performance</a>, on price for a complete 3rd. I paid $1150 last may for a 5.29/ARB 3rd member. You will have to ship a core to them, or pay more.

I am not sure where you are located, but here is a listing from Craigslist in Placerville, Ca for a set of 4.88 IFS front and rear ARB for $1k. I know you already have the front gears, but for $1k it would be hard to beat, or you if you are to far away, you could pick up a 4.87 diff from an auto truck/runner usually under $200, and run just the rear ARB until you determine if you need for a front locker. I know you want a front ARB as well, but going from open to rear ARB will be a night and day difference, and this route would save you an easy $1k.

I have a rear ARB in my '90 and I have never really found the need for adding a front one. I have an auto-locker in the front of my '91(came w/the gears), and a rear ARB, and even on the Rubicon I found the ARB rear was all I really needed. With the auto-locker upfront I have to tap the brakes to get it to engage, something I rarely think about doing, so I hardly use it.