I watched a show called, "The Last Sting Ray" several years ago. It was about a guy who purchased the last 67 Corvette made. It was a little rough, but it was a 435 HP 4 speed matching numbers car that would be worth a FORTUNE when done. The block was cracked, and he found a place that specialized in welding and restoring blocks. It wasn't cheap, but you have to decide how badly you want the original block in your car. Mike at MRL might know someone.