Not necessarily. The length of the motor is specific to the rifle/grip/config.
e.g.
AK - ver3 mechbox - short motor
M4 - ver2 mechbox - long motor
HK51 - ver2 mechbox - long motor
MP5 - ver2 mechbox - long motor
FAL - ver3 mechbox - mid? (might be short, can't remember) motor
Motors are the "same" in that the pinion gear is the same between them and the bevel gear is the same in the different mechboxes....but the lengths are obviously different.
Dunno what you're trying to do...but it sounds neat (or stupid
).