One of the problems you guys are going to run into, is that the actually focal length of a lens, and the marked focal length are seldom the same. Then your viewing/focusing lens has to be, within quite close tolerance, the same as the taking lens. Then you have to have a focusing scale to match the lens.
And what you actually get for all this work is a camera that is slightly better close up at wide apertures. I would suggest going through the photos on the 120 RF Folders forum to see how much difference there is between say, an 3 element lens and an Apo-Lanthar, which is considered one of the best lenses ever.
In fact, I would suggest that anyone who wants to talk intelligently about lens got through the sticky photo thread there. Then also remember that people with more expensive camera probably have access to higher quality scans than the folks with cheaper cameras have to make do with, which narrows the playing field even more.