Husky,
I don't think you're going to get much lighter than that 215 CID aluminum block. It's one of the smallest and lightest small block V8's ever made. Most of the components in that thing are modern, lightweight aftermarket pieces anyway. If he's got, say 100 lbs. of bar, chassis, etc. hanging on the basic engine, that puts its weight at about 400 lb. Pretty good power to weight ratio. More power isn't what is needed from what I've seen, watching it in person. The things got plenty of power, just not enough bite. It barely slows down in the wood. What's really needed is a way to get more bite without the added friction of the front of the saw slamming into the log as it tries to pull itself forward when the chain hits the wood. No two guys are capable of holding the thing back away from the log. Just my 2 cents.