John,
If that was an F that would make it a 1994 engine. The 6015 is a base engine. The following letters or numbers would indicate changes.
Example out of one of my Ford Engine Block books. C5ZE-6015
is a 1965 engine out of a Mustang (Z), and the (E) is just Ford engine engineering. 6015 states that is the base engine.
Ron
Try this link and seeif you can find more.
http://performanceunlimited.com/docu...rtnumbers/html