First of all, 550 is the right length (to not be sticking out the end).
Secondly, I hope pestobanana is right (about the barrel length), because I'd rather not take apart the gearbox, don't have the time.
About the spring/fps it has a QC spring change so I'm just gonna toss the spring in there and hope for the best

, I've found that my AK (completely stock CYMA, except for 470 fps spring, can outrange all my guns, even the G36c with TM cylinder set)
As far as the gears go, I don't think they matter to much for accuracy, as long as they don't break. Most of the stock gears i've seen seem fine, except for some crappy zamac ones from a sportline mp5k. Hopefully I wont have to buy a new set, but as for the piston head and air seal....really bursting my bubble here guys
I did some creative googling about the bridge hop, never heard of it before. Seems like a good idea, but it'd have to be shipped from Japan (the rest of the parts would take me like an hour to get and install) With the whole R-hop thing, I lOVE the idea, but I don't love the idea of someone doing it for me, does anyone know a link where I can order some? I'd be willing to order if its for an R-hop
Thanks for the feedback btw.