Sniff the plug to determine if it is gas or
oil. If it's
oil you could have either a defective intake gasket seal, bad valve seal(s) or guides, or the rings are not sealing properly. I have a 418 stroker that had
oil issues from an improperly installed intake gasket. Had to replace the gasket to reduce oil consumption. Any high oil consumption, as in 1 quart every 500 or so miles? My 418 stroker also had oil consumption problems and can be a bugger if the rings flutter at high rpm or are being pulled too deep into the cylinder bore. By the way, who built your motor?