MOSFET and LIPO will take care of the ROF. That gun has an M100 spring in it and shoots around 350fps, a LiPO and MOSFET shoul put you in the high 20's ROF.
Now you will need a little heavier spring to give you a little more power. An M120 at most since its not a reinforced gear box. An M110 will probably work fine and get you around 380+FPS.
A new TB barrel and hop-up bucking to increase your accuracy.
Give it to Fireman, he knows what to do with it.