May not help much in your situation, but I had a 350 block that cracked in a straight line about 2 or so inches down from the top of the deck.
It was in a pickup that I was driving and needed so I had to the best I could to get it going.
I cleaned the block the best I could, wire brushed the crack to clean it even more. Then I put JB weld on the block.
When I sold the truck 5 years later the guy that bought it drove it another 10 years without any trouble. Even then the patch was holding, he just flat wore out the engine. I'm not recommending the JB weld fix in your case, but the stuff does work well if everything is cleaned properly.
Is he certain it is a crack? I have seen a couple of 350 blocks that had what looked like cracks but were simply a casting mark.
