I just replaced the gearbox in my '60 S2. The speedometer hasn't worked in years and I took the opportunity to replace the cable as well. I hooked it up to the speedometer which tells me that I was going 65 MPH when my GPS said 42. I surely didn't feel like 65, much as I would like to believe it. The old gearbox had no letter suffix and the new one is "C". Are the speedometer drives different for the transmissions?
The old one was 151118640 and I replaced it with 25241474 C.