wiper problem

Hey a-body owners - I have a strange problem that is probably just a wrong part installed on my car. My drivers side wiper hits the upper windshield gasket while the passenger side clears it easily. Both arms are 15" Anco arms which is what the chart says to replace them with when I go to the Anco site. I can't find specs on wiper length in my manual, so I was wondering if anyone can tell me what's supposed to be on my 67 Barracuda.