Like some of the previous Replies, for 1965-66 I prefer the Rally Pac (picture of a '66 attached).
However, if you don't want to go that route, and go with just the tach, there aren't many options. Most, if not all, of the Rotunda and Cobra tachs came with only the dash (for usually near the speaker grill as has been mentioned) mounting bracket. If you wanted to mount the tach on the steering column, you had to purchase Kit C6AZ-17368-A separately for a whole $2.40 (picture attached). The 60's and at least some of the early 70's issues of this Kit came with the chrome bracket shown. However, the later issues replaced the chrome bracket with a 90°, "L" shaped, cad plated bracket. T%his Kit was finally shown as "NR" (Obsolete) by July of 1979. I have also attached a couple of the different Ford Mounting Instructions. Note that the mounting of both the Rotunda and Cobra tachs was via a 10-32 stud in the middle of the rear of the cup, and held on to the mounting bracket with a chrome acorn nut.
If you wanted to "splurge", and order the "top of the line" tach, the Sun Super Tach, you not only got the chrome mounting cup, but both the dash and steering column brackets. Note that the Sun tach used a mounting bracket with a much larger hole than the Rotunda and Cobra bracket. This was so that a threaded bushing (through which wires could pass) or a bolt could be used, both which threaded into a curved "nut plate", which allowed for unlimited positioning of the tach cup.
Interestingly, both the Ford and Sun tachs used the large worm type hose clamp to attach the brackets to the steering column. So if you see such an installation, don't let anyone tell you that the installation was "cobbled" together ; this is what was intended back then.
One other option on location of the tach which I have seen, is, if you have a console, mount the tach on the console, using the dash bracket, much like some of the GM cars had in the late sixties and early seventies.
Hope this gives you some ideas.
Bob