cranking compression is a good measure of the compatibility of a given combination. beyond that, it's not very useful as a diagnostic procedure. in school we had a 327 shivvie mule on a dyno that we conducted all manner of horrific and cruel experimentation. one of the pistons had a hole drilled in it (i think it was about 1/4 inch?). that cylinder had almost the same compression as the rest of them. learned a lot on that engine.