You'll probably be fine with 5 in the high pack and 4 in reverse, but if it was mine, I'd go with 6 and 6. Set the high pack with .080" clearance and the reverse with .100" and you'll be fine for sure. Drilling the case that way for a full tree brake should be fine, but you can score some instructions from Summit's website. Look up the brake and you can view the instructions online.....