I agree with s&wchad that you have a legitimate S&W factory made 5" field barrel for your model 41. The primary clue is the protruding crown on your muzzle. Some describe this as half doughnut or as a numbed barrel, but I've never seen this level of machining done on an aftermarket cut barrel.
The field barrel was approved by management on 5/8/1959 to be sold as a M41 with a five inch barrel or as an accessory for an existing pistol. The first model 41 with the field barrel was shipped on 9/2/1959. The field barrel was produced with many minor variations until it was discontinued in 1976. It was reintroduced as an accessory only in 1980 but was only available until inventory ran out sometime in the mid 1980's.
A best guess of your serial number would be 1967 or 68. S&W never made any attempt to manufacture, store, or ship their products in any kind of serial number order. The only way to accurately date your pistol is to request a letter from the Smith & Wesson Historical Association. They will give you the date shipped, who it was shipped to, and, most importantly, the barrel length it was shipped with.
More pictures would be nice.