Recently got one of those with the 24" barrel. I love it, and I think the machined in rail is one of the best features.
So.... why do you want 20 moa in your mount? I looked up that scope and it shows 100 moa or 27.8 mils of elevation. Assuming you can use half of that when mounted on a 0 moa rail, you have 50 moa or 13.9 mils of up elevation, which should take you out well past the supersonic range of any .308 Win load (most go subsonic at distances where you only need 8 to 10 mils). Are you going to be shooting beyond 1200 yards? Or doing all of your shooting at 1000+? If not, you should be fine, with that scope, using standard rings on the rail.