Marcus, the holes in the cover for the take down lever must not be all the same size. I tapped with 1/4-20 and the bolt is loose.
I have been thinking a little more and have come up with two more ideas. It seems like the ramps of the cover slide nicely under the ramps of the receiver up front by the carrier. As one would push the cover into those ramps, the cover would tighten. I have 2 ideas:
1: Remove cover. Grind down a flat in the takedown pin that would face forward when the t/d lever is in the up (to remove) position. Drill and tap the inside flat (facing the bolt)of the square lug that the t/d pin goes through. Install a 8/32 ball end set screw so it just protrudes into the t/d pin hole. Grinding the flat on the pin would provide relief for the protruding set screw and allow for easy take down. Replace cover and turn t/d lever down. Test for tight fit and adjust set screw as needed. Resulting interference would "jam" the cover into the "ramps" of the receiver and tighten up the whole thing.
2: Remove cover and pin. Shape a bit of steel to fit the machined out area forward of the pin area. Drill and tap for 1/4-20 button head. Secure threaded bit of steel into machined recess area ahead of t/d pin by mechanical means or weld in place
. Drill through hole in the back of the cover below the serial number, through the square lug. Install rear cover and tighten the bolt. This will force the cover forward engaging the ramps and tightening the cover in place.