"45 MPH" is a myth, sort of like the Easter Bunny, Santa Claus, and honest politicians. I owned a 1959 3800 for several years, with virtually the same 235 engine, SM 420 trans, 4.56 rear end, and 18" wheels that your 54 probably has. I had no problem cruising at 55-60 MPH, or more when necessary. I saw 65-70 on a downhill a few times, and the engine didn't come unglued. The truck will take it, if your tender ears can stand the noise. Yes, they make noise at speed- - - - -most people are just too timid to push the loud pedal.
Jerry
