Should have gotten template/instructions? Kanter website says it comes with template and instructions? What's up? This is tricky without a template or any other advice, so wait for someone to advise. My method is without any measurements available.
Take off inside lower windshield metal trim to get a little visibility. You won't be mounting on the actual A pillar upright, I don't think. Your approx. location as seen from outside of truck is 3" below windshield and 3" forward of door gap. You would tape the outside chrome bracket to a spot and the inside bracket taped to a location that looks like it will align with whatever angle the bracket holes aim. As said by Brad you should drill a small hole into truck sheet metal at center of one bracket arm hole and small hole in center of the other bracket control arm hole. Re-tape brackets in place and run a small rod thru to confirm that arm of light will be aimed as you thought. Then open arm holes (1/2" Dia?) and drill for bracket screws. Just be sure you place the trim brackets in the correct orientation for the shape of the body panel to which it is attached. You can practice on a wooden mockup if you are handy.
You place painters tape on painted metal and drill thru that. BUT ALL your holes with be covered by brackets anyway. The drilling won't cause paint to explode or pull a huge chip off, especially with sharp drills and gentle pressure and tape, No problem. Start small and increase a size or two to final diameter.
Link to a fellow doing it on a 60-63. Found on Stovebolt search, thanks to DADS50.
This may help you "see the light" 
