The T-clamps attach the little ladder beams to the case. This article shows a simple way to make using cold-forging/bending. An equally useful hot-forging method is described on the Forging T-clamps page.
The process step-by-step Edit
First make a model T-clamp for thin, easily bent steel (on the left). Once you've found the correct proportions, unfold it, cut slightly longer pieces of the thicker T-clamp steel (above). Bend these into U-shape while keeping a piece of the little ladder beam steel in between the halves. The results should similar to those in the picture on the right:
Attach the T-clamp to the vise, with the little ladder steel piece in between:
Bend the U into T-shape carefully using a hammer:f
The results should look like this: