Brett. I'm using a tripod mount ring attached to an aluminium bar/dovetail plate. A riser may be necessary to permit rotation of the camera for framing. Particularly, if the camera sits over the dovetail clamp, which is likely with camera/lens combination, to balance the DEC axis. This is OK with a small lens, but you may need to obtain a custom dovetail or drill and tap the holes yourself. Some dovetail bars come with numerous mounting options/attachment points/holes.
EDIT: OK. I don't know the ARCA, but I believe it's a dovetail. There are several dovetail clamps available. Just need to be sure it has the mounting holes for your EQ. Losmandy, Vixen,
http://www.robincasady.com/Astro/ http://admaccessories.com/D_Series_Saddles.htm