[Vicky]

We used a non-hardened 9/16 Bolt, tapped a 5/16 hole through the bolt, and taped the head for 1/4 NTPF.

The pictures are of our first bolt. I was somewhat concerned with how deep the NPTF went into the bolt (past the head). We then welded another head onto the bolt for more material, and made a new bolt similar to the one shown, but with the two bolt heads. The block was tapped for a standard 9/16 bolt.

That one is installed on the engine, (last picture), torqued to ~40 ft Lbs, and works fine.