Thanks for advice, I'll try to reverse polarity first :AOK
Its designed for 8 ohms, 16 ohms wont hurt the amp, just reduce its power by about half, so it wont overdrive the greenback. a tech can adjust the bias to get your power back for you, or you could just buy an 8 ohm greenback and save the money and trouble, if your testing the greenback, the amp wont drive it hard enough to hear the classic greenback tones, so not really getting the full range of test, green backs are great speakers, I would get the right though.
reverse the polarity on the speaker, its safe and easy, and generally gets you more better bass, and tone, you may find you have the speaker you want in the amp.