I do not have very much experience with working on airsoft guns but I have heard people say that installing gearboxes sometimes requires "modifications". Specifically I am planning on installing a Polarstar engine into a PDW body but do not want to make "modifications" to the engine itself. Since a PDW is basically an M4 should I really have to worry about making major alterations? I am OK with dremeling or filing out the inside of the PDW body if the Polarstar engine does not fit. Is that probably what I would be able to do? Any suggestions would be appreciated.