I think the first digit of the serial number will indicate the year. My guess is mid-60s. If the first number is a "3", then it is a 63, "5" is 65, etc.
That's a cool old horn. I have a similar horn on my '64 Huffy built Firestone 500.
I thought your's was a '63. I had a mens maroon '63 with the same chainguard/decal. Not sure what else you can find on the serial number. I like the 60's Huffy middleweights. I think they went to the canti frame in '59 maybe? I have a '58 ElDorado that is the single bar.
Just picked up this same bike - The "rack" on the back of the bike is really thin and doesn't have any loops or anything. Can panniers actually be used with it? I can't see any way to really secure them!