Started on my super six swap today. And as expected I had many a sheared bolt when removing the manifolds. Most I'm pretty comfortable drilling and tapping or just drilling and use a long bolt+nut.

But the one that concerns me is of the 3 bolts which fasten in intake and exhaust together, the odd one out which doesn't pass through the exhaust manifold sheared. I'm wondering about much depth I have to drill and tap that as I don't want to penetrate into the exhaust manifold interior.

I was amused though that with nearly every bolt possible shearing, the heat riser worked smooth as butter.

After reading your post I measured a manifold I had on a shelf that I had drilled out . I was able to get a bottom tap to a depth of 15/16 " . Hope this helps.