defroster duct work

I agrae with the person that gave u. u advise.these as all old mopars and cars . r common.changing size will not help flow may make faster as u feel. but heet at a slower speed . will b more the slower the air passes heater core it collects or gathers heat. and god as my whitneness.
have fun. lie 2 your self. then ask I DO OWN A MOPAR. help is free.