I added a chute to my 5.8 recently. The holes in the bow are pretty easy - just drill, pack with epoxy putty and then drill a smaller hole through the putty once it sets. Can't recollect what size the holes are, but i can check if you're interested.

For the pole length, I wouldn't cut it until you test-rig the boat. Leave it at 20' in length, but rig the boat as if it was 12' in length. Then run the chute up and see how things look. Don't cut it until you get things looking right. For the record, the pole on my 5.8 is 12.5' long, 0.065 wall T6061.