The Speed Graphic:

the mystery solved thanks to those nice guys at www.graflex.org . My thanks to Dann Fromm, 45PSS and the others who helped explain my camera's oddities.

The back on the camera appears to have an after sales modified spring kit to admit a roll film holder. Obviously this makes it a bit tricky to use other lenses, without a ground glass to focus on. However its perfectly serviceable with its current lens and rangefinder setup.

The lens is 1938 and although the manual is newer, the camera itself is likely to have been produced in a batch in 1940. So now I know.

see:

http://www.graflex.org/helpboard/viewtopic.php?t=5928

I need to check the RF and try a roll or two now and see if the holder is OK !