In the world of AEG, we have FAMAS replicas primarily from TM (and Cybergun). All these FAMAS replicas are V1 mechbox based and are in fact highly upgradeable both FPS-wise and ROF-wise if you know the tricks.
The FAMAS offers great ROF because it has a different gear ratio (check its spur gear and bevel gear). On the other hand, it is NOT true that the FAMAS lacks internal parts. In fact, most parts inside a V2 mechbox can be installed into the FAMAS V1 mechbox. The FAMAS mechbox can use the V2 gears, piston, cylinder, spring and nozzle without any problem. All that you need to worry about is the motor and the spring guide, but the spring guide is difficult to break (unless you go over 400fps), and the motor is widely available out there.
Frankly, internal parts compatibility is NOT an issue for FAMAS. In fact, the FAMAS is a very solid AEG and an ideal candidate for power upgrade.
It is true that you have less external accessories to play with. However, the plastic FAMAS has a very sturdy structure. It is not fragile at all. In fact, the real steel FAMAS uses plastic housing as well!
The TM FAMAS implementation uses a 2-halves gun frame design – the mechbox is being sandwiched in the middle. The stock gear ratio is of a high speed one, therefore it is less forgiving for the motor (that’s why your motor will have a tough time pushing the gears when a harder spring is installed). To power a harder spring, you need to switch back to the “normal” gear ratio by replacing the spur gear and the bevel gear.
