1958 235 engine
This engine doesn't have a oil filter. These old engines used mostly non-detergent oil. If you ran a cleaning solution through the engine can you imagine all the sludge and grime that would flow through the oil passages. I think I read before about the oil passages in the rear of the motor getting plugged up. I would clean everything up the best I could. Blow air through the oil galleries then drop the oil pan and clean it real good. I would buy a new set of lifters and install them. I would use a straight 30w non-detergent oil like they used back in the day.