Beautiful song! Now is the time for you to learn the idiom, "to blow hot and cold". It means "to be enthusiastic one moment and not interested the next". Here is the link to British and American dictionary definitions: http://idioms.thefreedictionary.com/blow+hot+and+cold Similar constructions include "to search high and low" and "to go hot and cold". These are perfectly correct. On this basis, "the autumn winds blow chilly and cold" is perfectly fine.

It's not as fixed as you assume. It is possible to use an adjective in the position of an adverb - these are called "flat adverbs" - so I see no problem with the word-order of the sentence. It just sounds a little poetic. The main thing is the rhythm of the line, "the AU-tumn WINDS blow CHIL-ly and COLD": [ . - . - . - .. - ] This is a typical poetic rhythm in English, and I think that was the first thing in mind before being fussy about grammar.

Chilly and cold are modifying "winds" (adjectives)... yes, this structure is for the lyrical benefit. I dont know if this structure is grammatically correct, but it is used sometimes.... particularly in songs/poems and expressions.

"Garfunkel" - please note correct spelling.