Welding the block ?

But that wasn't your question, was it? If I was determined to try a fix, I think I'd clean the hole out very good and then work toward closing the damaged area and the bolt hole up with JB Weld until I got it small enough that it could be drilled and tapped for a head bolt. In tapping the hole I would work the tap in very slow and keep the threads cleaned off with compressed air.

The main thing is to take your time and clean the work area thoroughly before starting, insure you fill all holes when using the JB Weld and make sure there are no gaps or air pockets, as these will be leaks later.

I would again iterate that I would not change the current method which is working holding things together. The only reason I would consider the repair I described is to try as a last ditch effort to save the block if the current method failed to hold.

Good luck.

Mike

With all that said, my advice is unless you've gotten the whole engine tore down, and are prepared to look for another block if you get bad results..... ..... .. leave it alone!!!!!

If it is really unusable, maybe you'd be time and money ahead to find a good used block, if you have the engine apart for repairs, anyway.