The mighty mounts work only on some Yakima and Thule carriers. It all depends if the load bars pass through like of the fork mount bike carriers. Sounds like WetMutt encountered this type of carrier.
Horizontal part #2-90116-905-0 for bikes
Vertical part #2-90116-821-0 for snow boards, skis

I think this is what's included in the kit http://www.vehicross.info/downloads/vx_roof_rack.pdf