340 block value?

FWIW, for those who want to sonic test their own blocks, I have found and use a decent and (relatively) affordable sonic tester; look up TM-8812.

You carefully have to file off some material either side of the transducer gap running down the middle of the test head (being very careful to never touch the gap itself with the file) to make it conform to a round cylinder. But one that is done, you are in business. Adjust the velocity factor to get the right thickness readings on a piece of cast iron that you can directly measure (like a cast brake rotor). I have measured wall thicknesses with this tool and then double-checked the thickness with mechanical means and it is accurate within a few thousandths.

Simple white lithium grease works 100% fine as a sonic media between the sonic tester head and the material under test.

BTW, you guys would freak over the wall thickness of Opel 1.9L blocks.... .300" on the major and minor thrust faces is the average LOL. Plus an unsupported bore wall length of under 5".... overbore heaven!