That little bit of the piston at tdc, you can use a marker to mark. then take off the jug, grab the piston off the con rod, and trim it off. You can ramp the exhaust side of the piston if you want it to open soon and wider. Thing is I recommend reading about ramping and porting before you try it. Understand what you are doing and why. Then decide if you want to port and/or ramp. The trimming of the tiny bit of the bottom of the piston at tdc blocking the intake port, isn't going to hurt anything but will give ya a little more power from better flow.
DO NOT CUT ANY OF THE PISTON SKIRT OFF THE EXHAUST SIDE. YOUR ENGINE WILL NOT RUN IF THE EXHAUST SIDE OF THE PISTON SKIRT IS REMOVED.