The program cover for Super Bowl XII between the Dallas Cowboys and the Denver Broncos is seen on January 15, 1978. (National Football League)

Denver Broncos guard Paul Howard (60) knocks down Dallas Cowboys defensive tackle Jethro Pugh (75) during Super Bowl XII on Jan. 15, 1978, at the Louisiana Superdome in New Orleans. (Tony Tomsic via AP)

Dallas Cowboys wide receiver Butch Johnson (86) celebrates in the end zone after scoring a 45-yard touchdown reception against the Denver Broncos in Super Bowl XII on Jan. 15, 1978, at the Louisiana Superdome in New Orleans. (Tony Tomsic via AP)

Denver Broncos quarterback Craig Morton (7) prepares to hand the ball off against the Dallas Cowboys in Super Bowl XII on January 15, 1978 at the Louisiana Superdome in New Orleans, Louisiana. (AP Photo/Vernon Biever)

Dallas Cowboys defensive end Ed Jones (72) tries to take down Denver Broncos running back John Keyworth in a 27-10 win over the Denver Broncos in Super Bowl XII on Jan. 15, 1978 at Lousiana Superdome. (AP Photo/Vernon Biever)

A Dallas Cowboys cheerleaders poses for a photograph during Super Bowl XII against the Denver Broncos, in New Orleans, Jan. 16, 1978. (Associated Press)

Dallas Cowboys wide receiver Butch Johnson (86) hauls in a long pass from Roger Staubach for a touchdown against the Denver Broncos in Super Bowl XII on January 15, 1978. (Associated Press)

Dallas Cowboys quarterback Roger Staubach (12) throws a pass against the Denver Broncos during Super Bowl XII on Jan. 15, 1978, at the Louisiana Superdome in New Orleans. (Tony Tomsic via AP)

Dallas Cowboys linebacker Mike Hegman (58) celebrates against the Denver Broncos in Super Bowl XII on January 15, 1978 at the Louisiana Superdome. (National Football League)

Dallas Cowboys running back Tony Dorsett (33) runs downfield against the Denver Broncos in Super Bowl XII on January 15, 1978 at the Louisiana Superdome. (National Football League)

Dallas Cowboys quarterback Roger Staubach avoids a sack by Denver Broncos defensive end Lyle Alzado in Super Bowl XII on January 15, 1978 at the Louisiana Superdome. (National Football League)

Halftime festivities are seen during Super Bowl XII between the the Dallas Cowboys and the Denver Broncos in New Orleans, Louisiana on January 15, 1978. (National Football League)

Dallas running back Tony Dorsett walks off the field after helping his team defeat the Denver Broncos in Super Bowl XII, on January 16, 1978, in New Orleans. (Associated Press)

Texas E. Schramm, president and general manager of the Dallas Cowboys, left, and running back Tony Dorsett smile in the locker room after defeating the Denver Broncos 27-10 in Super Bowl XII in New Orleans, Jan. 16, 1978. (Associated Press)

Dallas Cowboys head coach Tom Landry is carried off the field after helping his team defeat the Denver Broncos in Super Bowl XII, on January 15, 1978, in New Orleans. (Associated Press)

A detail view of the Super Bowl XII ring of the Dallas Cowboys is seen in 1978. (National Football League)