You could use heat tape to plug the holes, added wood would make it nose heavy. Most of the heat off the engine should exit through the bottom of youe cowel. You might want to reinforce the engine box where it comes together at the fire wall for added straigth with thin CA. saturate the area with thin CA until it won;t soak it up anymore. I also used small triangle stock. Don't get crazy with it because you want to keep your nose weight down.
NEDYOB