My rallye gauges came with a clock. I never use a tach on this car or any other really, I just rev it until it sounds like it should go into the next higher gear, but thanks for the reference!
I was referencing the tach as an fyi that they do that as well. Dad had both his tach AND his 150 speedo with trip odo calibrated by them. They can do what you are asking, here is their link. They have a TON of parts speedos etc to help