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Can't we just drop one out of a low flying plane?

That looks identical to the Chevrolet left hand box.

I notice the adjustment screw is down pretty far. That one might be worn out, unless it is properly adjusted now.

You could also look for a RHD Chevy car box if they have them in your part of the world. Also I think a LHD Chevy pickup box might work too. They bolt up on the right hand side.