When did prevost switch from the AD-9 to the Wabco 1200 series? and now they have kit

So my chassis is a 99, last of the ol XL breed... according to Prevost Nashville, it came standard with a 1200 series drier. ( crap since I just sourced a rebuilt AD-9 24v Unit since my blow off valve was malfunctioning....) so today I discovered, yeah, this AD-9 won't fit in the spot the other one is and it appear to be factory... so back to the drawing board. Again Prevost then said, Hey we have a retrofit kit for an AD-9 to go in there....

So i'm confused, the early XL had AD-9 then maybe for space? they went to the 1200 series, now they have a kit to refit the AD-9? and I'm guessing because of the 3/4 inlet/outlets? and not the 1/2 on the other? strange that the lines are all 3/4 lines lol.... not sure Prevost engineering got this one right.

anyone shed any light on this?