If you can't raise the tank, lower the engine. If your Nobler is the ARF version, this is kind of a common problem. Mount the engine on 1/8" aluminum pads, and test fly with out the cowl. If it reacts the way you want, you may try thinner pads, or shim the tank with 1/32" shims.
A round 4 ounce Sullivan tank may work for you, fits up between the motor mounts a bit more, and you can rotate the stopper a bit also in the direction you need to go. This is what I did on one of my son's ARF Noblers to get the run correct. Once you have teh run even, than you can re-work the cowl or make a new one.
Type at you later,
Dan McEntee