There is an easy way to mount a cowled engine. You will need to restrain the fuse in the upright position (with the nose pointing up). with the engine installed on the mounts set it on the firewall and now place the cowl over the engine. You can now move the engine around to where it is centered perfect in the cowl opening. After you have determined the correct place to mount the engine, remove the cowl and mark your holes for the engine mount. Remove the engine, drill your holes and install your engine. It will turn out perfect. On smaller planes I have suspended it from the edge of my work bench with the landing gear laying on my workbench and some sort of weights on the gear. On larger planes that are to long for my work bench I hang the plane on something tall like a dresser. I have used this method for years and it has yet to let me down.