The usual "crack spot" on 57 and later nailheads. (doesn't commonly happen on the 264/322.) Typical on boat engines and engines that have been left neglected out doors with water in the jacket, which froze, resulting in this crack. As you can imagine, this perticular one, wasn't visible until block got tanked. More often than not, the crack is obvious, and can span anywhere from 2 inch's, to all the way across the bottom of the water jacket. Always pull the starter and look, upon purchasing a core to rebuild. I've also seen all kinds of different repairs. The only "correct" way to fix it, in my opinion, is "pin it" which is very expensive and usually makes more sense to just start with a better block that doesn't have any strikes against it. Welding it isn't a considerable option in my opinion. Once the head is bolted on, there is constant stress, trying to pull the weld apart. welding it with a torque plate or cylinder head bolted on, would relieve some of that stress at the weld itself, but what about where the crack starts and ends? Just not worth the risk (especially if you're a shop and building the engine for a customer and have to guarantee the build, as we do), considering the big overall expense to rebuild one of these engines, or any other vintage engine for that matter. A lot of machinists are all about "bill-able time" and not looking out for whats best for the customer. i commonly hear about people being advised by shops to dump more money than its worth into a part that should've be thrown away, instead of starting over fresh with a better core. its up to you to stay educated and review all your options, and whats most cost efficient, and what will result in a much better final product. i realize blocks and other considered "core parts" are not as easily obtainable in other countries across the world.