Thanks. I have been thinking of it on and off for quite a while. I wanted to come up with something easy and cheap to make without any special tools, and scalable for whatever application. I think this fits the bill fairly well.
I started working on the block tonight. I have some 1/8" x 3/4" angle aluminum. Its not really what I wanted to use (I was thinking of 1/16" x 1/2" angle.), but it should work.
I started with cutting out the top lengths, and then the side lengths. I just used a hacksaw with a metal blade and clamped it in my vise. Make sure to use the smooth side of your reversible jaws, the jagged side will eat up the surface of the aluminum very quickly.
Then, I measured down 7/8" on each side and cut along the inside edge of the material. 7/8" ended up being more than enough, but gave me the overall length I wanted which was 4".
Using the vise, I bent each of the tabs inward.
Then, I cut the excess length off the ends. I'll cut the remaining excess off the tabs once I get farther along.
Then I did a test fit. It looks pretty good. My two side pieces are a little off. Bending is quite hard to get them the same length. But, I can shave a bit off the long one with a file and use a hammer to bend the tabs down a bit more.