It may be shorter than the rest, but there's a bolt under the mast step. Check the last pic and look for the loner up front.
Not sure if it would have made a difference, but last spring there was the beginning of a bulge. Lead was in tact, epoxy coating had cracked. We took advice to sand it down and epoxy then paint. End of the season it looked the same. This spring was the damage. So in hindsight, it would have been worth the effort to drill into the bulge last year and try to drain any water. Then seal the keel bolt with caulk/epoxy. Prevent more water from travelling down the bolt. Or at least create an exit at the bulge each winter. Water isn't a problem as the bolts are stainless, freezing is the only issue.
My other suggestion for you is any time you really torque your keel on anything like running aground, dry out your bilge and caulk around your bolts just in case. If it was a really big hit, maybe even remove/losen the nuts one by one and rebed the washers, but that would be a pretty big task. But there's no way to know water's getting down the bolt. And I'm told most folks don't get a warning bulge. And since this repair will end up well into 5 figures, it might be worth the preventative effort. We never hit anything, I still think our bolt was an oddball. The other nine nuts were still on tight.
That alternate fix you mentioned was plan A. Boat yard was thinking of that but it's too big an area to fill w/ epoxy/mastik. So the good fix is the same but forging lead around the bolt again. More $$$ but it's going home to it's creator as it turns out so it will be as good or better than new.
If you want to see where your keel was made, I'm told they did all the keels for Tartan into the 90's.
http://www.marskeel.com/