What year is 351 windsor d9te-6059-b?

D4DE = first manufactured in 1974, for the Falcon, granada, or LTD, and it is an engine part.
6075BA = an engine block with BA modifications.
5D3= ?march 3rd 1975.
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d9te-6059-b
d9=79
te=what the engine was origonally designed for
6059= the part casting number
b=modifications to the casting block from the origonal design

http://www.webanswers.com/automobiles/how-do-i-find-the-year-a-302-for d-engine-was-made-and-what-car-it-is-from-756bc8

The "d" indicates the decade of the 70"s and the "9" the 9th year of the decade... so 1979. However if this is a casting number (in other words it is raised up and cast in the block) then that simply indicates the first year that casting was put into production not necessarily the year it was produced. If it is a stamped number then it should be the year it was manufactured.