When building to save weight first thing is to get good, accurate scales that will weight ounces and one that weighs pounds. It is nice to place a part on the scales that weights 4.0 oz, drill holes and lighten until it drops to 2.0 oz or less. Does not sound like much but it all adds up. Heaviest single item is the engine. The wheels, tires, brakes are something where many pounds can be saved, but the smaller, lighter tires only last me about 5 hours, this is an area for some good weight savings.