CA M15A4 to DMR

[Shift77x]

Ive just got this CA M15A4 and its pretty much stock. I got a prometheus 509 TTB in it now, as well as a guarder 1 peice hop up but it still has the crappy little CA yellow plastic gears on it. And from what ive heard the GB has a S100 Modify. Looking to make it a DMR I was going to just get a drop in G&P 8mm rienforced gear box that apparently ships with a 150% spring which they say will shoot a .2 at 400fps. I was going to put in a m140 high torque motor to go with the box just because I heard that the high torque will have a quicker response time then the higher speed m120 that you would think would go with the gearbox. I wouldnt even closely consider myself a gunsmith at all. But I feel confident that I could put in a drop in gearbox myself. Just looking for a little insight as to if this sounds good or not.