huffy serial number location?

[idiotboy]

Hi guys new here, bought what i believe to be an early to mid 60s huffy eldorado this weekend, paid 25 bucks and probly got ripped off! im gonna throw some grease and spray paint on it and ride it around town. Can anyone tell me where to find the serial number on these frames? its not on the bottom bracket tube like my modern bikes.... thanks in advance

 

[schwinnless]

Check the drop outs, prolly left 1?

Or headtube also.