So, I have this real old Aria guitar. I've been trying to find out what year it was, but the only information I have on it is the serial number and model number. As far as I know, Aria didn't start to use serial numbers much until mid-70's or so, I'm thinking this one is from the 60's. I could use some help trying to locate the manufacture date, google isn't helping much.
Model number : A551B
Serial number : 4218
Anyone have an idea?

Thanks!
EJ