Now that I am home and can look at the pictures on something larger than my Blackberry, it appears the crack may have been caused by a variance in the aluminum or residual stress left in the part during casting after the core had degraded. Either way, I don't think that repairing the cylinders by welding or cast welding is a reasonable option. You may be able to use a structural adhesive to repair them, but since the cylinder have been fired, there is a good chance that ally has absorbed enough of it's surrounds to make an adhesive solution hit or miss. If Calvin has a good enough relationship with his casting vendor I am sure they can work something out. If not, and I were Calvin, that cylinder block would be going up my casting vendor's ass.
On a side note, find a decent casting house in North America is pretty rough. I am not sure that I can even think of one worth talking about. The Union Foundary in Bellingham, WA is the best I have used in North America thus far, but their capabilities are a bit limited and they usually have a very high work load making ski boat propellers. Edelbrock has a great, recently expanded, casting facility, but I would be willing to bet that they make alot of internal scrap that they don't tell anyone about. Besides that, Edelbrock doesn't really do work for anyone outside of Edelbrock. Japan has several great cating houses, but they are long lead time, expensive places. Germany has a few good places as well, but they can be tough to deal with sometimes. As I get further away from my old job, I should be able to start sharing more about some of the inside racing industry stuff.
Good luck getting this sorted out. If I can be of any help, give a shout.