I like the idea of hiding some of the structure to mimic a m66 mount. Part of my attraction to the Deuce is keeping it looking like a military truck.A 4th leg on a m66 ring mount may work pretty good, and still keep the military look.
You are going to need some triangulation to get the strength you need, but as long as it looks like something the military would have made as a NEW m66 ring support, I think it would sell.
As for marketing/liability you are just selling a replacement m66 mounting system. i.e., no implied ROPS ability would even be listed.