I'm thinking that 48 is how many miles between gas stops. Since it isn't a springer and the engine isn't a flathead or Panhead, it has nothing to do with a '48 Harley. They only mention the torque, maybe it has 48 HP? Maybe it burns/leaks 48 quarts between oil changes?

Let's hope there's intelligent life somewhere in space 'cause it's buggar all down here. -- Monte Python