Brown Trout re strange pre-10
This is some information from "A History of Smith & Wesson" by Roy Jinks, along with some "informed estimates".
On March 11, 1940 S&W began making Military & Police revolvers for British Commonwealth nations then at war with Germany. They were chambered for the .38 S&W cartridge. Since the British service load was a 200 gr. lead roundnose bullet they were often referred to as .38/200 British service revolvers.
They were made in 4, 5, and 6" barrel lengths. Initially, from March 11, 1940 to December 4, 1941, they had the same high-polish bright blue finish as regular commercial S&Ws. From Dec 4, 1941 to April 10, 1942 they had a brushed blue finish. After April 10 1942 they had a parkerized finish.
The company was making 6,000 to 7,000 of these revolvers a month. On April 24, 1942 the M&P serial numbers reached 999999. S&W started over again at s/n 1, with a "V" (for victory) prefix.
Doing the arithmetic, take 999999, deduct 857200, and divide by (we'll estimate) 6,500 revolvers made per month, and we can estimate your revolver was made about 22 months before the V prefix was introduced on April 24, 1942, or roughly June/July 1940.
Obviously we don't know exactly how many revolvers were made each month so this is only an estimate, but it is a reasonable estimate.
After the war Britain was desperately in need of foreign exchange to rebuild its country and repay war debts. Thousands of military arms (e.g. Lee-Enfields and S&W revolvers) were exported to Commonwealth nations (Australia, Canada, New Zealand) and to the U.S.
Many of the S&W .38 S&W revolvers were rechambered before export to accept the much more popular (in the U.S.) .38 Special cartridge by firms such as Parker-Hale and Cogswell & Harrison. Also, many which were exported still in the original .38 S&W chambering were later rechambered to .38 Special by U.S. gunsmiths.
The conversion was not a very good idea. The .38 Special cartridge is longer, has more case capacity, and in factory loads is generally more powerful than the .38 S&W cartridge. It is also a bit smaller in diameter, fits loosely in lengthened .38 S&W chambers, and expands considerably on firing. It's a conversion no responsible company or gunsmith would ever consider doing today.
It was common in the 1950s and '60s to see these revolvers advertised with barrels shortened and a new front sight installed. I guess the idea was to make them look more like the S&W Chiefs Special and Colt Detective Special revolvers which were very popular at the time (and still are, for that matter).
To address your question "is it rare or a chopped up classic", from the information you've provided I'd lean to a "chopped up classic" opinion.