The T-53 ALREADY has the reduction gearbox, and is only about the size of a normal V8 engine, everyday rain should not be a problem, since they are flowin in the rain at several hundred mph in planes and slightly less than 200 mph in helos, I know the H-3 uses a splashguard for its intakes, but you would need some kind of cover anyhow to keep the debris from the road out of the engine. One small pebble kicked up into your intake would destroy the engine.