You're going to want some new gears, I know Guarder for sure makes torque up gears for a version 7 gearbox, Prometheus might as well, but you'll have to be careful because TM and G&G M14s aren't cross compatible. Also, you're going to want a new Guarder Infinite torque or Systema Magnum motor. New wiring with a mosfet, and possibly a tightbore as well.
Also, from personal experience, I can tell you that a G&G M14 is a COMPLETE bitch to work on. The the only gun within my team that I hate to work on, so keep that in mind before you make any decisions.