Spring Upgrade

I was wondering would this gun be ready for a spring upgrade? Say to a 120? I haven't upgraded anything else except for the barrel, so it's basically all still stock. I read that it has reinforced gears, receiver, etc., but I'm still not sure. Is there anything that I should upgrade before I go putting in a new spring?

http://www.airsoftstation.com/tsd-tactical-gen-ii-sr36kv.html

It should say all of the things that it comes with stock through the link.

And if I do go about upgrading the spring, where do I start in terms of learning how? Never actually opened the gearbox before, so not too sure as to what I'm doing.

Any help is greatly appreciated, thanks!

i doubt having an m120 in it would be overkill for a gun like that. But as a guideline you usually want to upgrade the spring guide and piston and anything else thats connected to those parts. However you say you never opened up a gear box before so i would consult with a tech while doing this.

Well there aren't exactly any local airsoft retailers/stores around, but I assume it would be worth my while to go out of town to one so I make sure I don't mess anything up? (and to make sure my gun is ready for upgrading in the first place)

Www.airsoftSMITH.com
They'll do some good upgrades for ya

Wait I couldn't really determine by their website, but would they do things where you send them your gun, they upgrade it for you and they send it back?

Yessir theyre doing that for me as we speak. I heard they do a very good job.

Just wondering, 380FPS stock is quite respectable, why would you want to drop in a M120 ??