I doubt that. I don't believe the LBP 7 1/4 came out until a few years later. In 73 you would get a 7 1/4 when you got drum front brakes and a 8 1/4 when you got disk front brakes. It would be more likely that someone upgraded your vehicle to front disk brakes, but didn't want to spend the additional money to upgrade the rear axle.
