Ok here is what I see. You can replace the mount with one better suited for the 120. Being a single peice mount it will be a tad lighter. When mounting the engine, drill and tap the mount that would save the large watchers and nuts. 6-32 screws for both the mount and engine are plenty. Try a Vess or Xoar wood 15X8 and the Dubro plastic spinners with aluminum backplate are about the lightest you can get but hold together. The biggest weight loss would be the cowl. Contact Fiberglass specialties and see what a fiberglass peice would weigh. You may be able to drop a few oz there. Being a pumped engine is the fuel tank as far back as you can get it? And lastly, this has little to do with weight but do yourself a favor and get rid of the fuel valve. Sooner or later it's going to be an air leak valve.