Where is the number 3 piston on a 5.4 liter Triton v8 engine?

On a 5.4L Triton V8 engine, the number 3 piston is located in the right cylinder bank (as viewed from the driver's seat), second cylinder from the front. The firing order influences the numbering, so it's not necessarily the third cylinder physically from the front. You'll need a diagram or the engine's service manual to be certain of its precise location in relation to other components.