Shifty, a third block reading 7004013 means your engine was made on 1 April 1970. Your mower was probably made later in the same year.
If you post some details of the engine's issues in the Questions on Briggs & Stratton Engines sub-forum, we can go through a diagnostic procedure to figure out how to get it into top-notch shape. Just make very sure its sump is full of oil before you continue to gather information - it makes no sense to risk wrecking the engine now that it's survived for more than 40 years.
