For starters I have to tell you, 550 fps is not something you can easily just "Lego build" together. It sounds to me like you just want to have the max FPS you are allowed to have, and that isn't always easy or the best.
For starters, the version 2 gearbox shell has a major flaw in its design. The corner of the cylinder is near the step in the bottom of the shell. It commonly cracks there and basically blows the front of the gear box shell off. If you have never heard of that just search "cracked V2" on Google and you will find plenty of examples. There are ways to help prevent it, but they require opening the shell. Can you work on a gearbox? Have you tried assembling one with an M170?
Notice how Evike says "Super reinforced enhanced" gearbox? That is a marketing ploy to get you to buy it. Also notice how they call it a "Systema/G&P/Classic Army enhanced "Thick type" shell"? They are trying to get you to associate that box with those big name brands. If you haven't noticed almost every airsoft item is "reinfoced". It's a buzz word that makes people think they are stronger. You can buy reinforced everything from gear box shells to pistol grips, to flash hiders. There is a difference between regular V2 shells and reinforced shells, but I think only TM ever made non reinforced ones. There are actual reinforced items, but that shell looks like every other reinforced one that I have seen. If you want a strong V2 track down an MTHaynes. Lastly, I would never use bearings in a 550fps build. I don't care if they are 8mm or 9mm. At those forces always use hard bushings.
Also, "Lipo ready" is just straight BS. Do you know how many Amps your motor will be drawing to pull back that 550fps spring? It says "steel gears" but I don't see what ratio. If you run that box with a lipo you will burn up your contacts fast (I also question if a 9.6 would even cycle it). You need a MOSFET to protect them, and you need a MOSFET rated to handle the Amps you will be pulling. Also, don't buy airsoft lipos. Do your research and buy a hobby grade lipo. They are generally cheaper or equal in price but perform WAY better.
That charger, is crap. I'm not sure if you are aware of it but lipo batteries are sort of dangerous. They can potentially burst into flames if there are problems. If you aren't buying a charger capable of testing the battery, you honestly won't know if it is safe to charge. I use the Hyperion Eos6060i ($110) and highly recommend it. It will check the lipo and make sure it is safe to charge and prevent overcharging, and it has REAL balance charging. Those cheap chargers check that the total output of the battery is equal to 11.1 volts. That's not good enough. If one cell drops to 1.8v and the others are at 4.2 volts, that lipo is gonna blow. The Hyperion actually balances each cell to proper voltage. I used a cheap ACM "lipo balance charger" to charge a lipo, then plugged it into my Hyperion, and the Hyperion refused to charge it because the cells were all out of whack.
I have to be honest with you. It sounds like you want a Barret .50 cal that shoots the hottest it can to impress other people. That's fine and all, but you are dealing with some pretty big stuff that it sounds like you don't understand. I'm pointing this out to you because I don't want you to burn your house down with a junk lipo setup or blow $150 on a gear box that (to me) seems like a waste of time.
If you want a reliable Snow Wolf M82 at 550, go polar star. That's what I'm doing.
