When I replaced my mast step with a welded aluminum one made from 1/2" plate, two of the galvanized bolts came out and 2 didn't, shearing off the heads.
Since the step had slotted holes, I just drilled new holes for the SS lag bolts.
Be VERY careful drilling lead, as it can gall up and sieze and break the drill bit. Go very slow, backing out the bit very often to allow the flutes on the bit to unload.