I have a RockyMounts pitchfork that I used to use on a VW rack. It has the plate on the front that slides into the channel on the crossbar and you tighten it down with an Allen key.
I have someone interested in buying it but they have a OEM Subaru rack with elliptical bars and no channel slide the plate into.
Is there an economical adapter that can make my bike tray work with his roof rack?