be sure to allow engine to sit for a few minutes before checking oil, better yet check after it has been off for serval hours. if it shows normal level when cold and overfull when engine is hot check for plugged oil passages
I had a 327 impala once, was running rough, took it for a tune up, still the same , turned out i had overfilled it with oil, drained some out, ran fine , guess the crankshaft was hitting the oil in the pan