Very similar to the Tier One you have been looking at;
Spartan Sling Point Rail.
www.uttings.co.uk
Actual photo of the product itself;
This is a simple picatinny rail.Attach it to your riflestock, use it to secure bipods or flashlights etc.
salamandertactical.com
You will need to attach it with an M5 countersunk bolt into the existing threaded insert, (where the current sling stud resides), and an extra shorter M5 countersunk bolt plus nut & washer passing through the stock and forend grip, (new hole required

).
All assuming it's a Tikka that your working on?
PS The base of the item is not perfectly flat but ever so slightly radiused however, so is the Tikka forends and forend accessory grips.