Personaly I would take the head off and check that the 2 Head shims are fitted (a 0.1mm Brass and a 0.3mm Aluminium) before you fire her up. If they aint then fit them they are needed to stop the piston slapping the head, But if they are there go for it and fire her up using the fuel you intend to run on. Dont bother running in on lower nitro content, this engine needs to be run on 25% for best performance. The Scratch sounds more like a mark from a screwdriver blade used to push the Piston down from TDC during manufacture. I've heard of them doing that before. Those dodgy Chineese.