The Smiths speedo listed for the 1957 GF has the numbers you posted except for the last alpha character which should be "L" rather than "N".
Re the distance difference: do the speed readings correspond correctly with the distance readings? If you drive the instrument with a lathe or drill press at, say, 30 mph for 60 seconds, the odometers should register one-half mile. If you're not sure of the origin of the instrument, it might be that someone tried to set the odo back which would have damaged it.
The Smiths chrono is a mess of small springs, wheels and ratchets, and its calibration is best left to the experts.