Ditch the M7 and get a M700. The mag length is shorter in a M7. Bolt-on parts are very plentiful for M700 especially if you go the tactical route.
I love my M7s for hunting. But for modifications the M700 is the way to go.
You can rebarrel to a varmint profile and run an off the shelf HS stock inletted for the varmint barrel but OAL of cartridges will be short and I'm not sure anybody makes a DM set-up for M7s if you need more than 4 rounds.