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The "E1" identifies it as - the year the cast was released to production - 1981. Doesn't mean you couldn't have this casting in a '84 or '85 truck either. It's just the date iw was released. The other numbers I believe are month and plant??
It is a 1981 design truck engine block;
E1 = 1981 design
TE = Truck/Engine
6015 = Engine Block
AA = Revision number
The E1 number would be used until there was some significant redesign of the part. For example; Mustang HO engines from 1987 through 1995 all used the E7TE (truck!) cylinder head. If you want to know when the engine was actually made, look for another number that will be the casting date, usually four digits.