I'm trying to find a viewing prism that will flip the image on the ground glass right side up. Anyone know where I can get one?

Commercial solutions are mirror boxes (not prisms) from Linhof, Calumet, Horseman and Toyo... expect to pay around $200 on Ebay. When find the time I'll make a 2X3 version for my Century...the only part I've not figured out is the viewing optic (I'd prefer folding binoculars, like on the beautifully executed, compactly folding Rolleiflex periscope viewer)... will probably have to be trial and error.