Have only done the parcel tray in my 77 so far, but will see if I can find some from when I did my 51 chev. The PVC foamboard was bit of a game changer in that it's soooo easy to work with. From memory it was actually cheaper than hardboard too. It's often referred to by different trade names such as sunboard, palight, sintra, foamex etc and most plastics places will have it. Signwriters also use it a lot.