Each model Hugo Meyer rangefinders were made for 1 focal length only. The focal length it is made for should be stamped on the back of the RF along with the model number. A 4C is for a 127mm/5 inch lens. They should have enough adjustment latitude to cover the focal length tolerance range of lens from the era in which they were made.
I do not know what focal length yours were made for.
I serviced a Anniversary Speed that had a 4C Hugo Meyer RF and a 135mm Xenar that was optically 131mm to 132mm and the 4C just adjusted to match it, the close distance setting was at the extreme limit of the adjustment.
The major difference mechanically will be the shape of the internal operating arm, equivalent of a cam.
www.graflex.org/helpboard/viewtopic.php?t=6319
