Plastiguage is great stuff. I never did real well with a mike, so untill digital calipers came out, I plastiguaged it. It was more of a go-no go situation. I remember back then, stuffing a 318 into a Dart in shop class. We got several engines donated, took them apart, swapped parts untill we got a good engine. New bearings, rings. We did the head work. It took all school year, but it eventually ran, and ran for some time.
The auto parts store down the street does not carry it. It has to be ordered.