Dan Banjok made a Fox 70 from two Fox 35s. It lines up back engine/front engine, nose of engine in back connected to crank of engine in front. Great sound, turns a 12 inch prop. The separate crankcases/needlevalves are retained. Double the power of a single Fox 35? Definitely double the power of many Foxes I've seen tuned to do a 4/2 sloppy rich. This engine sounds more like a twin Foxberg setup. It pulls around a ridiculously heavy big Profile Corsair. It is Dan's second build up. The first made it through 17 flights before the rear crank snapped. The new one looks more promising. Dan increased the diameter of the rear crank (I think), lapped the crank into a newly machined bushing, and improved the metallurgy on the pin that connects the front and rear engines. He probably did a lot else. This engine cranks. Puts out power. And weighs I imagine, about the same as 2 Fox 35s.