I know I am not answering you direct question here, but why not look into a Pertronix conversion to your old points? It will allow you to go to fully electronic ignition, use your same distributor that you have now, and the tach will keep on working just like it does now.
The swap will take a Saturday afternoon, require some basic tools and a bench vise, and cost under $100.
You can buy them at Summit racing and many other places. I installed one a couple of months ago along with Garin1 on his 68 convertible. Pretty straight forward operation, and even if you are going NCRS with the car, the experts will have a hard time telling you are sporting dependable electronic spark.