Ac/heat duckwork.

[Oldtimer48]

Hello.
I have an 84 Skyline that we just purchased.
I've discovered the jackass that installed the dryer vented it straight through the heating/ac duckwork. Now the heat goes under the home instead of towards the back half of the home .
Can I cut out the bad section which is only 8 to 10 inches and install I new piece and where can I buy a replacement.
Thanks.