To echo BigC, yes 2 18650 cells will fit in a 2D M@G. You will need a sleeve to keep the cells centered. If you search this forum you'll find all the info you need.
I have made a spacer to keep the cells centered so that is not a problem. I am guessing I just have to relocate the spring to the bottom cap, and remove the anodizing.
As an Amazon Associate we earn from qualifying purchases. Product prices and availability are accurate as of the date/time indicated and are subject to change.
Using a KD golden shorty spring I can fit 2 of KDs 32600 cells, that gives me a good couple of hours run time from a ROP low bulb. I can get over an hour from a ROP high bulb, but have to use unprotected cells so they will turn on the high bulb.