Jim- My brother and I were racing full size OPC Tunnels back in the 70's and we saw these twin vees almost every weekend and knew the drivers and owners . There were 3-4 of these rigs that showed up at the races we were attending and all of them were a little different as far as engine angles and spacing so apparently they were searching for the best set-up but I don't know what that was. They all ran great. Common sense would say to keep the props far enough apart to prevent the wash from interfering with each other. I would make the motor mounts adjustable (up-down) and just experiment to find what works the best. I have never worked with a twin vee so I have no real answers but maybe someone else on here can help. Remember-testing is part of the fun-especially when you find the right set-up.