The serial number should be on a metal plate attached to the front of the firewall. It also could be stamped on the engine block toward the front, just below the head gasket, or on the bell-housing near the starter.
6015 was Ford's casting number for engine blocks. The E27N in front says it was for the E27N. Other numbers might relate to the date of pouring or the ID of the wooden casting pattern. (They probably had many duplicates)