You don't say what model years your Discos are, but you should be able to swap SLABS units freely among them, at least for the purpose of your intended testing. There were at least three versions of the DII SLABS computer.

There was a recall of the SLABS from at least the '99s and 2000s I recall, and later another version with different programming was installed at the factory in the '03s and '04s. Two of the three part numbers are SRD500070 ('03-'04s) and SRD000070 (earlier models). But again, for your limited purposes you should be able to swap them freely.

There is no vehicle-specific programming as there is with the BCU. As others have mentioned there is a SLS/Coils setting in the SLABS but if all your trucks have coils in the back they're interchangeable. Even if you put an SLS (air springs) SLABS in a truck with coil springs it would be fine for a short time for your purposes.