Howdy,
I have an extra lens board for my early-model Gowlandflex 4x5 (see pic), and I'd like to procure a cheaper lens with wider aperture to use for focusing. G-flexes typically have a better-quality taking lens (e.g. Symmar) and a lesser but faster focuser (e.g. Xenar). I wish to use a 240mm Apo Ronar as the taker, and something like a Sironar or maybe Apo Rodagon (both 6 elements, 4 groups) for the focuser. Or maybe a non-Rodenstock, with 4 elements in 4 groups, like the Apo Ronar. Since the G-flex has no movements, image circle is not a great consideration, and since I generally stop down to 11 and smaller, exact focal length match is no big deal either.