OK, I sent my first sonic checker back. It did not have a "cast iron" setting and it would not change the numbers as you ran the probe up and down the bore.
I knew that once you got near the top it had to get thicker near the deck but the numbers did not change.
So I did not trust it and sent it back.
I bought this one.
https://www.ebay.com/itm/314314770567
It has 3 different cast iron settings so I gave it a shot.
Just went out and checked #1 cylinder. It would change as you moved it down the cylinder so I felt better about it. This one takes oil on the probe where the other one used water.
The thinnest spot on my .060 over 67 2 bolt 400 block was .157 between the bores. The outside was all over .200 as was the front of the cylinder. The inside was very thick, in the low .300s.
If the other holes are like this I can take this thing .100 over and still have .137 between the bores .
But I would take a minimal amount on the worst bore.
What is considered minimal thickness on a non thrust surface ?
I have always wanted to weld a KRE lifter bore brace into this thing, put some ductile iron Milodon splayed caps with 4" crank. Kinda like the ultimate stock block "440".
I would want to practice ni welding steel to lifter bores on a junk block first. See if its doable.