I believe the 3.73 gears use the same carrier as the 3.55's and lower in the Dana 30 making the carrier break between 3.73 and 4.10. For the Dana 35 the break is between 3.55 and 3.73.
Either way, if his jeep has the stock gears it will be either 3.55 or 3.07 both using the same carrier.
As for the thickness... the gear sets are setup to be a specific thickness to match that given dimensions so there really isn't "thick" or "thin" sets available for these axles.
As was said earlier... the lunchbox locker install is pretty much the same no matter what.