Tony,
Your M41 likely was shipped in the summer of 1958. Because S&W didn't ship in number order, that's as close a guestimate as you can get without a letter from Roy Jinks.
The 5 1/2" heavy barrel was approved by S&W management on Aug 26, 1963 and the earliest I see on my database was shipped in late 1964.
I think the change to the ampersand was in the late sixties or early seventies but I don't have any real data on that.
If it really bothers you, find an earlier barrel and if doesn't you have a very fine pistol to shoot and enjoy!
Your M41 came from the factory with a 7 3/8" barrel with the muzzle break as that was the only option available in 1958.