You can shim the top cover at the rear or add a shim to the rear trunnion vertical stop ledge to tighten the top cover fitment. Just another option.
A spot welder and a strip of receiver stub at the rear downturn on the cover.
A recent pic of a sort of similar thing but done for a different reason. It extends to the cover bottom area. Yours need not be this large of course.
Spot welded to the cover.