Went on a Ford dealership’s parts website and they only had one part listed for the rear, and then went to a different site and they had 2. Don’t see how it would make any difference as all of the aftermarket manufacturers sell one rear shock for both cab stylesNot sure where you got the part numbers but I see 2 for the shocks.
BL3Z-18125-K - supercrew
BL3Z-18125-L - supercab
I doubt there is much difference but there is some. My guess is because of weight.
Great deal and GLWS.