Matt, yes the same concept would work with press braking thinner metals. If you search for "press brake tonnage chart" In Google, you get plenty of charts that tell you how much force it takes to bend your metal based on thickness and how wide your lower die opening is. Multiply that force by the feet in width your metal is. Not sure you will easily generate enough force without hydraulics though.
If by manual brake you mean a lever style brake (not a press style) you could probably make that do a radius as well, just increase the spacing on the pivot for the lever and use a thick "clamp" piece with a quarter round milled into it. That way as you bend it pulls the metal up and a round the round part but the pivot has to leave room to not bind.
For a real shade-tree experience, one can clamp the sheet metal to a section of pipe, of proper radius, then use a rawhide mallet to pound the sheet around the curve.
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