Gary,
Any of the older S-6 (6 inch) or H-1 (5 inch) will work, depending on what your car had (6 inch, I believe). The shaft lengths on the CV and Caprice lights are longer than what the Mustangs took (as Bernie pointed out), but they can be switched out. Internally, if you are using the red bulb it's probably a dual filament bulb (4416, like what CHP used). There is a piece you can buy and wire it to make it work right (I'll get the name and a part number for you later, if you need it)
