Yep on the right side mirrored to the spring/bb on the left. Then make it so your bb sticks up half of whatever the gap is on the left side. You could also use a pin like j427x did. I'd use a ss pin and bevel and smooth the face thats going to contact the receiver so it doesn't dig in. He epoxyed his in with JB weld which would keep it solid. With a bb it wouldn't need to be epoxyed, but it might be harder to drill the pocket depth that precisely.