For the passenger side mirror, CJponyparts has a series of pictures and words for the installation. They can be found at “cjponyparts.com/mustang-passengers-side-mirror-kit-1967-1968-installation”
Here are the instructions after the mounting holes have been installed. I have added some words for clarification.
10. Test fit the Mustang exterior mirror, but just snug it up. It will need to come back off to do the final adjustments.
11. Loosen the adjustment screw to angle the mirror in and level the top. This screw is the one visible when the mirror is installed. A phillips screw driver is used to make this adjustment. There is another adjustment screw located inside the stem for the mirror. This adjustment is done later and will be done using a flat tip screw driver.
12. Get in the car and check the view.
13. Take the mirror off and loosen the screw inside the stem and rotate the head toward the driver.
14. The head should rotate approximately 30 degrees.
15. Reattach the mirror and check the view again.
16. Remove the mirror one last time and tighten up all the adjustment screws, then reattach and enjoy.