I'm going to say mid to late 1980's as they made the change from the E to the F S/N prefix at the start of the 1989 production year (Nov 1988).
As for what choke it is, are there any asterisk's stamped on the barrel by the receiver?
* = full choke
** = modified
*** = improved cylinder
**** = cylinder
If there's no asterisk stamp anywhere then it's also a full choke as at some point they simply stopped putting the one on to indicate full.
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