I am assembling a H9 Miss America P51 and I have come to a stand still. The SuperTigre 90 does not fit the engine mount supplied with the kit. When I try to line up the engine bolt holes with the mount holes on the mount, they do not overlap to allow a nut to go through due to the engine mount hitting the metal of the crankcase. What can I do?

Maybe you could take a file or a dremal tool and remove the edge that touches.

As Someday said
Take a dremel tool or if you have a tabletop belt sander and put a @1/16 to 1/8 inch angle on the engine mounts this is what i have done to my h9 mounts in the planes tha i run super tigres in

I also have dremeled out an angle on the mounts to make engines seat better on the mount. Should be okay.