.60 overbore on a 1968 340

always better to check it first with sonic, rather than poke and hope

just make sure they calibrate the sonic tester. I can make a wall measuring .050" sonic test at .150" by purposely mis-calibrating the tester

the block has to be measured somewhere with a mechanical gauge, then the sonic tester used on the same spot, then the "calibrate" mode entered on the tester, and the value moved up or down to equal the actual dimension measured with the mechanical gauge.

then the tester checked again

then it's ready to go

if they just grab the gauge and test block after block, regardless of make or material, it's not going to be correct. aluminum, magnesium, cast iron, steel, etc. all have their own velocities to be calibrated for. it's the same type of technology used in the medical field for doing ultrasounds