340 valvetrain help

I would pull the valve covers and make sure the rockers are not hitting the valve covers first. Then look and make sure the pushrods are not rubbing the heads. If everything checks out good there, crank the engine and make sure you have oil coming from the rocker arms. If it doesn't look to be oiling good you may have to pull the rocker shafts and make sure they are turned correctly. I mention this because you said the previous owner said he had put in new lifters.