This is how I did my rear anchor, and it works like a charm. “L” shaped bracket made out of stainless steel and a pin welded to the vertical that is the same diameter as the rear cleaning port on the receiver.I get Zero flex.
The rifle is definitely competitive out to 200 yards using Wolf Match. I am using a Kidd 20” stainless, threaded, and Kidd back bores them like Anschutz does. I have zero complaints with the build.