They may have both 4x2 and 4x4 trannies available. The pictures at the bottom are of two different trannies; the first is of a 4x4 unit and the second is of a 4x2 unit.
I would contact the seller and ask for a confirmation that, if you buy one, you'll end up with a 4x4 tranny. While a divorced case setup could be done, it'd be a huge PITA...especially since dropping a 4x4 ZF in place of a T-19 is such a (relatively) simple task.
A 4x4 ZF will bolt up...you'll need a new clutch assembly (I would recommend a LuK SMFW conversion kit, since you'll need to buy a flywheel anyways) and floor pan insert, and I would recommend a crossmember out of a ZF truck (although, in retrospect, I think I might have been able to use my T-19 crossmember in my conversion, but I didn't have enough time to find out, so I can't say whether it'll work or not, and IMHO better safe than sorry). The 4x4 ZF is the exact same length as the 4x4 T-19, so you won't have to do any driveshaft modifications, especially if you use the 13-45 transfer case that's currently behind your T-19 (I think that the yokes are bigger on the 13-56, requiring custom U-joints or modified driveshafts).
I did a T-19 to ZF5 conversion a little over a year ago, and I imagine it'll pay for itself pretty soon with how ridiculous fuel prices are getting to be. Certainly, it's paid for itself in terms of drivability!!
I need to get my write-up done... *sigh*
school!!