You're likely never going to find a used battery tray for these 50yr old trucks, just get a brand new universal one
All the old trays are long gone. Most all rusted out completely. Universal or custom built is about your only option
You should try Yoda Jim's salvage yard- he has four or five 1977 pickups that he is parting out. He is in Colorado, and his telephone is (303) 506-5119. I agree it is unlikely that any battery trays have not rusted, but the one on mine had not and only required some Lawson's rust convertor- it even still has the plastic mat in the bottom!