Any ideas on this 340 block ?

I bet that's a unique set of cylinder heads on that one what with the water cooled exhaust manifolds. That may be really good if it's like some marine blocks and cast thicker, but it can also be really bad if there's a ton of scale that comes out of the water jackets and leaves the cylinders thin from both sides. The bad part would be having to invest in cleaning it before paying to get it sonic tested...