Here's a sketch of what I was thinking of making:
The lathe isn't shown; it would take too long to draw. The shelf is 68" tall. I'm 6'-2" so it's reachable while allowing me to open the belt guards on my machine. I thought I might add a lip, but it's not shown in this sketch.
The reddish brown panel is peg board. It doesn't go all the way down because it's 24" tall and about 3.5 feet wide. I can buy a smaller piece this way and save some money. I'm trying to avoid buying a full 8' x 4' sheet.
Thought I'd hang the various wrenches, chuck keys, etc. on it. I also thought I might make some tool holder like AGCB97, but that might be pushing it with weight. Thoughts?
I think I can attach the 2x4's with bolts to the back of the bench. I'd use 3/4" diameter conduit tubing as a spacer so I can tighten the bolts. The 2x4's would be snug against the table edge on the back and the spacers would allow me to tighten the bolts snug against the metal bench. I hope this makes sense. Zoom in on the picture to see how it's assembled.
I could add a 3rd 2x4 in the middle. This would allow me to add a smaller shelf below the larger one, since there is some space.
I'd like to keep this simple for now; I thought I'd try this and see how it went, then make any modifications. At some point, I could rebuild it with all the mods.