Accu-Swing Valve for 310SG

I just heard about these old add-on Accu-Swing valves for reducing the famous overswing of the 310SG backhoe. Do they work? Has anyone got a picture of the valve mounted? ....or know anything about how they operate?
Thanks,
rScotty working a: JD310SG 4wd w/extendahoe & 5600 hrs. Very nice machine..

Accu-Swing Valve for 310SG