Thanks for your replies!!! That was a HUGE help and really gave me the full story! The gap is like a half-inch wide forward tapering to 0 aft, with rust staining the keel. The gap had been filled and who-knows what other maintenance, but the rust had me buggered. The bolts are S/S so I did not think that was the source, until now.
New plan. We intended to drop (lift the boat off) the keel a bit anyway, to facilitate cleaning and re-bedding the mating surfaces, but now maybe we'll open the gap a bit further to assess the health of the bolts. If we find any that are questionable, we'll drop it all the way so we can get at it. Then we'll cut the bad ones, flush with the top of the keel, dig into the lead around the bolts and install S/S coupling nuts and new bolt-tops, sealing, loc-tite-ing and re-filling the lead as needed. Re-bore the bolt holes only as needed to fit the shoulder of the coupling nuts. The keel nuts don't look to be backed by much more than standard S/S washers but I want to get some full-sized, (at least 1/4-inch thick S/S) plates to carry the load in the bilge.
Now that that's settled, I'm still wondering about torque and bedding recommendations.
"Who would go to sea for pleasure
would go to hell for pastime."