I've had a Moki 1.35 and OS 1.08 in 2 UCD's,both flew well,the weight was not a problem,so I think the OS 1.20 would be fine and if I remember correctly,its lighter than the older OS 1.08. They do fly OK with the 91 too,but if there wasnt too much difference in weight,I would go with the 1.20. Is there is only 2-4 ounces difference,the 1.20 will be best for hovering. If the fuel tank is mounted behind the firewall,no pump or pressure system needed. I mounted over CG,then use a fuel delivery system.I use nothing but Cline,they work well from a .40 up to 1.60.