Except that after the initial model, the PET's case was plastic, or rather, structural foam, with no shielding applied to it all.
Source? Every Commodore PET I've ever come across had a metal chassis. Commodore64s and VICs had plastic ones.
Interesting. I didn't know that.
After the initial 2001 model, Commodore used a mix of materials, with some models made of all metal and some of a metal/plastic hybrid (metal base, plastic top), according to this website: https://www.zimmers.net/cbmpics/cbm/PETx/petfaq.html (look for "WHAT MODELS OF THE PET ARE THERE?")