This is prob the wrong thread, but I figured taking out a half inch around the actual rod , then removing a layer of core around bolts would be more then enough. Plan on packing the void .
Seems to me if you had plans to go beyond that it would be just as easy to trace out the flange . Then remove the top layer of glass, and the core 1/8 " smaller then the flange with a dremel. Then poor epoxy flush.
Seems to me keeping the water out is the point , and it doesn't take more then a 1/4 layer of putty to do that. Am I wrong? I'm usually an overkill guy, but the list is getting long of projects to upgrade.