Approximately what year do you think the engine is?

That code was used in 1957 for:
F = Flint, MI engine plant
9 = September
04 = 4th
B = equipped with Powerglide transmission

Find and post the codes in the locations shown on this page:
http://www.1954advance-design.com/Web%20images/casting-code-photos/codes-ser-nums.html