I'm curious... no real experience with the machine or blocks in particular. But with $7600 on the line, is there a chance you could pull the motor, diassemble and repair the broken areas by welding?
A crack into the oil passageways (unless it's just the sump) probably couldn't be repaired that way, but it's not impossible to weld castings, just not fun. And you have to make sure you've ground out or drilled out the crack tip and properly prepared the weld. You may have to take a machining pass across the gasket face after welding to correct any distortion, as well. But if you're good with a wrench and know a good welder, this may be an alternative.
But like I said, I may be talking out of my hat. Still, I had a guy weld up my precious cast aluminum mower deck after I put a rock through it, and although it's not load bearing, it would appear that it could be load bearing, and that load bearing welds can be made in this fashion.
Best to you, hope it goes well (and cheap!)
Tom