Soft interior parts are available . Seat covers and some foam underlayment.
The door panels are almost 100% replaceable with affermarket.
The hard plastic interior parts with exception of the dashboard is not available
The rear quarter panels have been reproduced they are so bad it's better they don't exist.
That said. A pillar and c pillar, quarter panel, extensions under the rear window are not available for 71 to 73 cars. There are tons of little things not made also seat badges the metal c channel for the extension pieces the head liner metal covers.
The head liner and the sun visors and parts for the sun visors are made, and they are very nice.
It took me 1.5 years to replace my original ruined interior with fresh parts from various sources using both used and reproduction parts.
I'm still always adding to it and looking for more parts.
If anybody wants more info I've gone through all the repo parts for 71 to 73 cars and have pictures and I can give tips.