Add a new Systema Magnum Medium-type motor.
http://www.wgcshop.com/pcart/shopper...-M_srch_magnum
Add a Systema FTK, although you may want to swap out the spring:
http://www.wgcshop.com/pcart/shopper...K-12_srch_PSG1
Ditch the 9.6 volt battery, run a 7.4v (or 11.1v) LiPo running Dean's plugs and better wiring, wires soldered directly to the motor tabs.
Add a heat-resistant selector plate and lo-resistance trigger switch assembly as well as a MOSFET.
http://www.wgcshop.com/pcart/shopper...716_srch_psg-1
Get an afternarket metal body, outer barrel and cocking tube (all rare and perpetually out of stock), as the TM G3-series guns have notorious body/barrel wobble. Stiffening up the whole chassis will make it a lot more accurate.
http://www.airsoft-war4.com/details.php?pid=2340
http://www.wgcshop.com/pcart/shopper...3RCL_srch_psg1
http://redwolfairsoft.com/redwolf/ai...l?prodID=18088
Then pray you get the whole thing re-assembled right.