There is a poster in Boomhauer's living room of a naked woman laying on top of a sports car. Her foot hangs over the front bumper and she is touching the rear fin with her hand. This would make her 10 - 11 feet tall.
It's clearly implied that Hank and the guys graduated from high school in the seventies, yet when Bill runs off to join the Army, the Quarterflash song Harden My Heart can be heard. This song was released in 1981.
The episode "How to Fire a Rifle Without Really Trying" is about Hank being unable to shoot. But in the episode "Luanne's Saga" a skeet trophy from 1975 can be seen on the shelf in Hank's den.