I haven't contacted them, as their literature says to contact the airplane mfgr., which will be one of the next steps on the list. But I figured that contacting people who have actually hung zenairs on a model IV would be the way to go, rather than the McBeans, who probably have their hands full with the newer models, etc. I was just contacted by a person who gave me Paul Seehafer's phone number, and I'll call Paul, but that might be an imposition, so I'll wait a bit and see if he answers the group, then maybe the phone call will be in order.
Lynn