I'm about to go down this route too. My mast is getting pulled (for the first time!) on Tuesday 10/23. I plan to cut it shorter to remove the corrosion from the base of the mast, and have a new step fabricated to make up the difference.
From what I've been able to research, those are lag bolts that go thru the relatively thin fiberglass layer on top of the ballast and thread directly into the lead. There is no wood involved in that area.