What is this Carter BBD port for?

Do you have a factory service manual for a 67 Dodge. Mymopar.com has them free.

IMHO

I would set it up using the info for a 67 273

Not much smog control in 67 other than the CAP stuff which is mostly dist curve and timing and a valve to slow the return to base timing on deceleration.

That being said. I would cap off all ports that are not currently in use.