when I bought the d60 ARB air locker, there were 2 available on the webpage. RD35 and RD42.
RD35 is 35 spline chevy, dodge, ford apps, FF front
RD42 is 35 spline for ford rears, FF
IIRC, that is the breakdown.
So, I think there is a difference in the carrier itself.
Pretty sure the intall kits are the same though.