I am looking into getting a polar star setup. I don't want to buy the Pre-made gun and would prefer to find a gun and drop the fusion engine in. What do I need for the line that transfers the air. Also I don't know what gun I want to put it in. I want it to be an M4 variant but I don't want to pay to much for gun that I am just going to rip apart. Ideally I would like a VFC 416 but those are a bit to expensive for me, is the Dboys 416 good externally? What else do I need that I might not know about?