76 Tank sheet
 

I keep hearing about a tank sheet. Where would I find one on a 76. I just bought this car and it appears totally original including every nut, bolt, and cotter pin. The car only has 10,500 miles on it and I bought it from the original owner who stored it in a heated garage. The insurance appraiser said it is a survivor and he had never seen one in this condition. I have the original owners manual, warranty book, tire and battery warrantee but no tank sheet. Where would it be?