the ltm-m adaptor that came with your 21 should say whether it will also work on a 35mm -- for the M2, you need the proper adaptor to bring up the 35mm frame line. To check, put it on the lens -- any lens -- and put it on the camera -- look through viewfinder, if farthest outside frame line is what you see, it's the right one. You can tell which is the 35mm frame line by pulling the selector lever on the front of the camera towards the outside edges of the camera (left).

To check the rangefinder, put a lens on and focus at infinity -- at that distance (and pick something about half a mile away, not across the street) the images should coincide AND not be off vertically, although a tiny bit of vertical misallignment is acceptable and, with a bumped-around camera, sometimes unavoidable.