There is a chart in the factory manual showing how to mark a wall for aiming. Someone should have one for a '67-68. Mine is for '65-66. Not sure it is the same. Blue masking tape on the wall works fine. Then just park and aim. Good Luck.
SWMBO's '66 Coupe 289, 2-V, C-4(Pony Interior, Rally Pac, A/C & Tiffany Stripe) & An absolutely rust free '65 289-2V C-4 coupe project now UPGRADED to about 99.78%. Now only a few more days. Only took 13+ years.