Yikes! That's a lot more info than I was expecting. I learned a lot. I now know everything there is to know about the old tachs. My concern at this point is the size of the tachs. I'm not sure I want to put a full size tach on the steering column, and have to move it off to the side, and I'm not going to drill any holes in the dash. I have a friend has a nice used Sun tach, that I can use, but the large diameter has me thinking twice.
I have a set of 2 silver face Autometer under the dash, for water temp, & oil pressure. Autometer makes a 2&5/8 dia silver face tach, that goes with that set. Certainly not the old school look I was asking about, but I may go that route for now. Thanks again for all the comments. When my head stops spinning, I can make an educated guess, as to what I want to do.
