Ok, with a 6.5cm diameter port you can tune down to about 23.5Hz in that enclosure, but using any normal 12" cone the port velocity will be too high & you'll get compression & distortion (chuffing) at high volume levels
I'm assuming a 55L enclosure due to volume loss of the bass driver, port & midrange enclosure needed.
Still work to be done though, so don't give up for an instant