I installed the snorkel on my HZJ 71, and based on my previous experiences I did exactly this:
1. Transfer the template on to paper: paper is a lot more flexible than cardboard, and the template is designed to follow every curve on the quarter panel, so it is easier and more accurate if you have the template on paper
2. Place the template on the car: tape the template to the car and check and recheck to make sure everything is OK.
3. Mark the holes with a marker
4. Remove the template
5. Drill the holes: I first drilled the holes for the mounting studs then two small ones for the hole saw. Then I taped around the area where I would use the hole saw to avoid damaging the paint.
If you have experience working with a hole saw you know they tend to move a lot and make oval shaped holes. To avoid that here´s a tip:
In my case, the small drill bit that came in the center of the 3 1/4"hole saw was a 5/16". I took that one of the hole saw, place in the drill and drilled the two small holes for the center. Then I took a long 5/16" bolt (aprox. 3" long) and cutted the head off, so I could place it as the center guide in my hole saw. The advantage of doing this is that when you are drilling the big hole, your center is not going to "move" because the bolt can´t cut the metal (as opposed to the drill bit)
6. Finish the holes: with a small round file eliminate all the sharp edges and paint them. For the big hole I took a lenght of vacuum rubber hose, cut it in half, and placed it as a gasket (however, it is not necessary) See first attached image
7. Holes in the pillar: you have to drill three holes in the pillar to attach the snorkel. The best way to mark them is by fitting the snorkel and marking the place they should be at.
After you marked them take a look at the plastic plugs....they´re square, not round....so make a square hole. Drill 6 mm holes and square them with a small square file so everything can fit right. A little silicon and you´re finished....water tight!!! (See attached images)