VIN on my 1967 Glendale orbit

Hi guys!!!! Looking for help!!! I’m getting the plates on my 1967 Glendale orbit and I CANNOT for the life of me find the VIN ! I’ve looked all over the hitch/ tongue. No interior inside cupboards… I can only see the SERIAL number which is a stamped certificate on the backside(6 digits long versus 14 digit VIN) …. Anyone have a Glendale out there know where I can find a VIN if there is one? Or is the serial number that is 6 digits just what they did back in 67?????