The four hole gasket is what you want if you are looking for an original style gasket for an A-code Mustang. Good luck finding an OEM part, I couldn't find one. The closest after market gasket you will find is the FelPro, part number 60059 which is sold at auto parts stores and Mustang parts suppliers such as NPD. It fits like crap but many have successfully used it (see second picture). I decided to make my own with gasket material purchased at Pep Boys (see third picture). Be aware that if the spacer or carb base is warped, you may have sealing issues. Just to be sure, I sanded my carb spacer on both sides using 400 grit Emory cloth taped to a mirror (you can use glass too) to make sure it was perfectly flat (see fourth picture). I used the carb spacer as a template and cut the gasket with an X-Acto knife then sanded the edges with 150 and 400 grit sandpaper to clean up the edges and holes. Worked well for me.
Edit: I used the four hole gasket for carb to spacer and spacer to manifold.