I replaced the keel boats on a 1972 Ranger 26 in 1998. The bolts heads are recessed into the keel flange. I replaced mine with S/S slotted flat head bolts. In retrospect, I'd probably go with moly bolts if I did them again. We had no leakage problems, so I didn't monkey around with resealing the flange to hull joint. I just took off the nuts and used a sledge hammer and pin to drive out the old bolts. I cleaned up the holes and mating surface between the bolt head and flange. In replacing the bolts, I used a couple of wraps of cotton caulking material (don't have my Hamilton Marine catalog nearby or I could give the exact name)around where the shank joins the bolt head (that's what the original ones had on them)then put on 5200 on the bolt shank, inserted the bolt, flat head SS washer and nut and tightned them down. I finished by fairing the bolt recesses. Hope this helps.
