I really wanted to do as much as I could using tools and supplies that I had on hand, so here is what I did. I found a large bolt, don't know what size or anything just the biggest bolt I could find in my pile. I then took a drill bit, no idea what size just eyed it up to the bolt, looked like the right size. Drilled through the casting, then sprayed the hole with chain lube. Got the bolt positioned and started tightening, very carefully and slowly, with a socket and the bolt just tapped itself right in. I noticed how if I tightened the bolt too far, it might sink down into the recess and I might not be able to get it out, so I grabbed an axle nut and reamed it out with my drill so the bolt would fit through it. Then I filed the shoulders of the axle nut down so it would fit inside the recess. The axle nut is turned upside down so the flat part is against the edges of the recess, and prevents the plug bolt from being tightened down into the recess. It works, looks good, is clean, simple and the bolt holds. I just have to tighten it very carefully so that I don't over tighten it and crack the casting. But yes, I got the bolt in without a tap and without cracking the casting.