I can't offer much advice, since I have yet to tear into one of these engines, but I was thinking about something recently: The engine from a Datsun 240Z is very similar to the M130 (the heads and valvetrain, specifically, look virtually the same), so it might be worth asking someone who's squeezed some more power out of a Z (or a 510, which has a 4-cylinder version of the same engine) what kind of mods he'd recommend for the Benz.