[The Megan 2207]

I'm not sure why you're specifically referencing <R07-N>, as this part of the rule only deals with how far the "hard" or "soft" parts of the bumper can extend from the frame perimeter.

My team has used a very similar angle attachment method for the past few years, but instead of attaching the angle to the bumper, we attach it to the robot and attach the bumpers by bolting through the angle. We find this is easier than trying to blindly attach the bumpers through the c-channel kitbot frame (we usually use that for our chassis).

From my understanding of the bumper rules, a protruding bolt head is perfectly legal, as it would only extend under your robot's frame. We normally just use wood screws to hold the angle in place, and we've never had a problem with that.