I have just bought an RB Graflex Series D 4x5 (it hasn't reached me yet). As filmholders for this camera seem to be very rare, I was considering fitting a Graflok back from a Crown Graphic and making an appropriate adjustment to the register of the top focusing screen (possibly by raising this a few mm). Only problem - I've never heard of anyone doing this! Does anyone have experience of this or any knowledge as to why it would/would not work? Thanks in advance for alll info.