Does it have the OE axle shafts in it?

IF it does I would consider putting in the Superior shafts. As you may have heard... I broke an OE shaft in goneMOAB (I do have the Tcase gears though)

If it does have the 4.88 R&P then you can regear your H233B with the Nissan 4.90 OR replace the rear axle with one from an Xterra that already has the 4.90 gears in it.

If it only has 800 miles from the last rebuild I would guess that the seals and ball joints etc are in good shape.

How much are they asking?

Other costs to consider (aside from the basic kit)
Front Driveshaft
Front Coil Overs / Shocks
Rear Spring Pack
Front Sway Bar