Stevie, I moved you thread to the Decoding section, and yes, welcome to the site.
COPO5 is most likely some transmission other than what was approved by engineering. In this case it "should" have been a Powerglide. I don't have a lot of info on the COPO codes, but Kurt might and I'm sure he'll chime in shortly.
(and here's the POP)
By the way, from the 12437 VIN code, your car started life as a V8, not an L6 so the engine's been replaced. And from the POP, the engine suffix code of DC indicates the 307 engine with a Powerglide. The transmission code of COPO5 is a real head scratcher though. Maybe the Torque-Drive??? That would require approval since it was only available with the 6 cylinder. What does the transmission indicator on the column read?
Ed