It means that unless the engine was carefully blueprinted during machining, the pistons you have will not be yielding "as advertised". Nothing personal meant - it's just one of the problems of building a barnstormer 383 vs a 383. If the compression ratio was verified by measuring the chamber size and calculating the volume based on the piston in the bore, and the volume of the compressed gasket, then it was blueprinted. I think the choice of cams was unfortunate. I've run a .509 in a "plain" 383 and even with a 4* advancing it was not what it could have been. I would suggest you not worry about the power level at this point. It's fresh, put it in and in an A body you will have a smile on your face.