This isn't pretty guys, but it's simple & easy to make. And it works.
I had scrap 3/8" plywood lying around, Roto-zipped the outline of the action on two pieces.
Two more pieces with just the pin area zipped out. Glues the whole bundle together and squared it up.
Had to add veneer to make action flush (2nd time around I'd use pine or another soft wood for ease of planing/belt sanding.)
Piece of piano hinge secure to block & Lexan, drill pin holes.
$2.00 for Lexan
Had the piano hinge, I believe I paid $8-9.00 for a 4ft. hinge some time ago (make a half dozen more.)
You don't have to be too particular with cutting (obviously I wasn't,) as long as action hits in a few spots will stay secure. If there's too much slop, you can always slide a couple of small wedges between action and wall.
Sorry about the camera flash, should have shot it with camo paint., so I could sneak up on it.