For the brake, you can probably just drill out it's bore to accommodate the larger 7.62 bullet, as the brake should have minimal impact on ballistics. Of course, putting one on that is the right diameter is always an option too. But, hey, if I had a smaller brake laying about - why not drill out a larger bore in it for a project at hand? You might have to alter the ports some, as that cartridge expels considerably more gas than the AK round. Deflecting the gas out the sides of the brake is what's really behind how they work.
I'd be very interested in seeing how this turns out too, as that is definitely a gun that could benefit from a brake. Plus, Mosins are about as common as a milsurp series can get, so chopping on one a little bit isn't going to be like getting a lot closer to taking the last pristine one out of circulation forever. I've seen some interesting mods done to this gun elsewhere on the net as it is inexpensive and a rather accurate shooter.