Dating a Sunn Magna 2 X 15

[Evoken13]

No, i'm not looking for romantic advice regarding this cab as the subject might make it seem....

I have a Sunn Magna 2x15 bass cab....looks like it's from the early 70's. Silver grille, black badge w/silver lettering 

Serial # is C 004060

Anybody know what year this is from or, if its worth anything ?
It has 2 15" guitar speakers....origs are long gone

THANKS in advance   

[gray]

Sometimes the date of manufacture is on the inside of the cabinet. That's the case with my old 215.