I've had my 312 block tanked and manifluxed They found a crack by the passenger side below the lower motor mount hole. They pinned it and pressure tested it and said it was good. I still have a 292 block with rotating assembly. If it's a good 292 should I look into grinding the crank shaft and using the 292 bored out or going with the 312.

Six of one and half dozen of the other.  If the machine shop is comfortable with the repair, that block should be fine.  The 292/312 mix is also a good way to go, but at this point will cost you a few more bucks to have the crank prepared.  You could also have the 292 block align bored for the 312 crank as another alternative.  Your call, but I don't think you can go wrong either way.

John - "The Hoosier Hurricane"

I just had the same type crack on a 272 I just had bored. Had it welded but havent reassembled it yet. I dont see any problem running it that way. I'll know next spring if it leaks.

Dan      Kingman Az.      86409