Ford offered a hood-mounted dealer-installed tach. You see them on some Boss 302s. If you can find one, it would set you back a couple hundred bucks. However, the dash-installed tach on the 69 would require you to pull your lower dash wiring harness and substitute a "tach dash" harness, plus changeout the printed circuit and the gauges in your instrument cluster, which would set you back around $450-$500 or so. I went the latter route, before learning about the hood mounted tach. If I had it to do over again, I would go with the hood-mounted tach. Way cheaper and looks cool. just my 2 cents worth. good luck.
sure it's fun, but it's only a car.