The Ares G36 uses a unique variation of the G36 V3 gearbox since it uses a microswitch trigger and has a piston spring release mechanism. With these enhancements, it uses a non-standard G36 selector plate and mounting bracket. To install a V3 PolarStar Fusion Engine into the Ares G36 and use the mounting bracket that comes with the stock gearbox, additional holes will need to be drilled and tapped on the right side of the V3 Fusion Engine. The Ares G36 also uses a non-standard selector plate which is held in place using two mounting screws, so a standard G36 selector plate is needed to use with the V3 Fusion Engine. Additional modifications include sanding down the safe mode cam so it clears the trigger and adding an extra support brace to keep the selector plate from getting jammed. The fire select switch can pull the selector plate too far back and it will sometimes drop off the support brace. The extra support keeps the selector plate in the proper position.
UPDATE: I have a custom G36 Fusion Engine selector plate that can be used which works better with the Fusion Engine. Click here