Look at the weakest link in the entire system...
...it's probably the point where the cleat attaches to the fiberglass. I don't think your Bruce is going to bend or crack before something else breaks, even with a hole drilled in it. I drilled a 1/2" hole in the center of the shank on both a 33lb. and 44lb. Bruce for my boat, in order to accomodate the holding pin. I needed the 1/2" hole to allow for the pin and the little locking piece to easily fit. I used a drill press, as the hole was right on the angled portion of the shank in the center and would want to walk all over the place if done by hand. Go slow, use cutting fluid. I'm not concerned about integrity of such a beefy anchor!Good luck!Trevor