You're certainly right, in the example above "below" is not functioning as a noun. I was only answering BitBlaster's comment in which he claimed that "below" only ever functions as an adverb or adjective, which is demonstrably false.

In the original example, "below" functions as an adjective and its placement is entirely correct, as far as I'm concerned, if a little unusual.

That isn't right. "Below" functions as a noun, too.
So "the below" means that which is below in the same way "the above" means that which is above.

Usage examples of "the above" are "none of the above" and "the above is Theseus's opinion" (William Blake).

Cf. http://www.merriam-webster.com/dictionary/below
and http://www.merriam-webster.com/dictionary/above