Leo - There are a few different vendors offering plastic ABS panel kits for the AD Panel trucks.
This basic kit from Ecklers
6 piece ceiling liner kit is one option.
This full blown kit from Josh's Muscle Car Parts
16 piece kit which includes panels for the doors, cab kick panel area and rear cargo area side panels is another option.
I'm not sure on your follow on question about the roof structure. Perhaps some fellow Panel and Suburban owners will chime in on that.
