Shown below is a copy of tank sticker I pulled off a 1970 Skylark. This factory documentation is located between the top of the gas tank and the anti-squeak mat.
You will have to drop the tank down several inches in order to get your hand between the tank and the mat to remove the sticker. In some instances, you may have to drop the tank completely. If so, remove all gas, disconnect all fuel lines and spray some penetrating oil on the strap bolts' threads. It would also be a good time to replace those existing rubber hoses with new ones. You can also replace the anti-squeak mat with 30lb roofing felt if the original one is bad.