Ive handled the gearboxes and shells before of both guns, with some handy machine / dremel work I've no doubt you could make it work.
That being said, CA did modify the design of their metal bodies at some point too. Earlier models required you to split open the upper receiver, current ones do not. The internal differences between each generation are unk. to me, as well as WHEN they switched designs. I just know that they did at some point.
