You must drill the hole in the fairing block first and use it as a guide so the hole in the hull is at the proper angle. I also alway drill from the inside out. This way I know nothing is in the way of the install or servicing of the ducer.
The Airmars come with the holes drilled already.
I would recommemd making a couple of "slugs" first out of foam material like the pink foam sheet for insulating a house. Make up 2 slugs out of foam the same dimensions as the fairing block. Then cut one of the slugs with the table saw first - this is the most fool proof way to do it as you can stick the foam slug on the hull after your cut to be absolutely sure you have the correct angle before you cut the acutal fairing block. If your angle is slightly off, adjust and cut into your second foam slug.
I did that first........with a piece of 4 x 4 I cut the angle and kept going back under the boat to check it until I was satisfied it was level.
It's very important, when you cut it to make sure the angle is on the correct side of the fairing block or it will be cut backwards.
With the block facing forward
the port side should be the lower side of the angle on the block if it will be installed on the starboard side of the boat.....and vise-versa for the port side of the boat.....but which ever side it goes on, make sure the block is facing forward
when you run it through the saw.
For the Airmar, they have a second bolt in front that locks the fairing block so it doesn't loosen and turn on ya, thats the forward guide..
Take the time and use scrap wood or styrofoam to make up a dummie block so your comfortable with the angle.
When your sure............let er rip.......