That's an elegant solution, Jakob. Kudos to John!
I would probably make them by hand from 3mm aluminium plate. Cut them out and drill them, then used either a hole saw or round file to make the large holes for the lower OTA. Aluminium is just that bit easier to work by hand
.
I think the final bends to shape could be done in a vice (i.e. bend to fit
).
Al.