The rack we had in our den when I was growing up (sorry, no pix) displayed 4 guns horizontally (so you can see the sides of the receivers, instead of looking at the floorplates)
Essentially, it was two vertical 1 X 4's with 1 X 4's set perpendicularly with cutouts for the guns. At the bottom was a drawer about 2 1/2 feet long which defined the bottom supports for the 1 X 4's. There was also a cross piece on the top.
A movable dowel was mounted vertically on the left hand support which was captured by the drawer. The drawer had a simple lock on it, which, when locked also secured the guns. Certainly not very robust, but perhaps enough to keep the grandkids from getting into them
