Are you sure it's a Rodagon 50mm f/4? I know Rodenstock makes Rodagon in 50mm but it's f/2.8. 80mm Rodagon, on the other hand is f/4. This may be why you are having trouble finding any information on it.

When buying a used enlarger lens, one of the factor to be really concerned about is condition of the lens. There are so many examples of "mint" lens out there that has awful fungus and haze inside. (I got one!)

I know nothing about Fuji but Rodagon is a well repsected top-level lens short of APO version of the same lens.