Stop or keep going?

The higher the nickle the thinner you can run the cyl wall and it is stronger.
I had a metal salvage yard I used to buy steel and aluminum for a little over salvage price but anyway he had a hand held x-ray gun that analyzed metal and told you the content of the metal, I ask him if he could check the nickle content of a couple blocks, he said he could. In the meantime his dad died he was like 90 and owned the business, after that his son never came back and auctioned off the scrap and property. I haven't found anyone around that has one, I think they are like $10,000.00 so not easy to find in my price range. I'm just curious if the 68 vs 79 blocks have more nickle, some say yes some say no but a friend of mine worked for Chrysler and he said they reduced the amount of nickle in 73 to save money.