Hey Ksd, hard to say, I would not pay for new bottom metal if you plan to change stocks.  Welcome to forum and I reccomend you get the new stock then have the bottom metal fitted.  Fore sure you should be able to have the ordered bottom metal fitted to many future stocks.

I installed the Atlasworxs BM in my t3x 300wm to be able to use the 3.715 AICS mag. It requires some use of a dremel as the AW part is wider than the Tikka Standard. I set it flush. No real instructions coming with the part. AICS mag doesn´t really work that well because the release of the round is a bit late, it will be even more apparent with a long round. Adjusting/opening the lips is one way to go, but really the lips are too long for the geometry.

Also, if loading long rounds you might need to adjust the receiver/ramp and notch it a bit or the bullet gets stuck under. That can also happen with the front part of follower in the mag. If not loading long ones you´d probably want to adress the follower instead of the receiver :).