Sonic checkers

I just bought a ultrasonic tester myself and it appears i'm going to have to buy a transducer/probe designed for cylinder or pipe inside measurement because the flat probe can't give an accurate reading in a curved cylinder..
You could probally remove the freeze plugs and measure from the outside of the cylinder inward through the hole,,but it limits the area you can measure to just that area..but it may be enough to give you an idea as to whether or not you can bore the engine over..