The odometer in the '51 has quit working. Of course, the '51 has an 80 mph speedo. I have a spare 90 mph speedo that I'm planning on fixing up to use. My question is are the gears in the transmission the same for the two different speedometers? Or, if I use the 90 mph speedo, am I going to wind up with a big error in its reading? Thanks in advance for the help!