Where are the #s on a 3.8 liter ford engine located, say somewhere around a 79-84 model?

[martin_werner2]

I cannot remeber what the engine came out of but it is a ford 1979-1984 3.8 L, 6cyl. I bought an idler arm for it and it did not fit. So the clerk said I need the engine #s off the Block. Where are they located at? Thanks Marty