Actually if it has One Gallon on it, the bottle is older than 1981. I would guess that it is from the 1970's. In the 1970's the regulations of many states losened up a bit and more states allowed the sale of whiskey in gallon bottles, thus the distillers started to bottle gallon bottles. Most of the gallon bottles usually came with a version of the "swing cradle" for easy handling of the pours. If the bottle is full, it has some fine Old Grand Dad bourbon in it. I would recommend drinkinking it. You will enjoy its complex, fruity and sweet flavor.
"Our people live almost exclusively on whiskey" - E H Taylor, Jr. 25 April 1873