Great how-to Wagonman. A couple items to add to this. Many Corvette aftermarket suppliers sell the number sets for '57 Corvettes that I would think are interchangeable with the tri-5 sets. Also, the internal gears are not available. I'm sure someone makes them, but they are not available to the public. I tried several speedometer repair and parts places to get one for our 57 Corvette, but all they will do is rebuild your unit. If you are lucky, you might be able to file down any bad spots on the gears to get them to run smoothly. It worked for me.
Ken

Thanks!! this we will help me a lot!! My speedometer is out of a 56, they looked the same from looking at the 57 pdf. My speedometer cable broke and I some plastics peices remains are still inside, I've read a thread to use a drill bit to remove the plastic pieces, drilled and removed some pieces, but when I stick a needle in it, I hit plastic still, I assume if im hitting plastic with a needle there are still remains of plastic pieces in the gear? Is it solid at the other end where the magnetic spins with the cable? What is the best way to remove the plastic pieces that broke inside? Thanks!