.50 CAL Ammo Box Stacker

I love the metal ammo boxes they are so durable and versatile, but why are they not stackable??? So, I made this Ammo Box stackers in two sizes. For the .50 CAL M2A1 and the .30 CAL M1919. I used the dimensions of the ammo boxes from Harbour Freight. The stacker is split in two pieces and the sides are different from each other. One fits on the lid of the box and the other side fits on the bottom of the box. See pictures which side goes where. Feedback would be appreciated, since I am a beginner and this is my first design from scratch :-)