In 1977 after giving up trying to find a gunsmith that would do the job, I installed an adjustable rear sight on a square butt 2" model 36 using only small files, a drill and a tap. The sight was long enough to cover up the bottom of the trough I filed in the top strap so it looked exactly like a factory installation. The job is easier than you might think because J frame adjustable sights don't have the square elevation nut that slips into a slot in the frame. For what its worth, maybe significantly less than a full 2 cents, considering the rarity of adjustable sighted 36s, the customized hammer and that the front sight is not factory, I doubt your target sight was installed at the factory, especially if its serial number does not date to 1975.

However, even believing it's not an original 36 target, I'd have bought it for $375. Two inch 36s are so common that none of 5Wire's $400 average price for for them is attributable to collector value. They're utility pocket guns, plain and simple. The custom work on yours adds utility value, so in my opinion, its worth at least as much as the most common variety of 36, even though the market for trail guns is much smaller than the market for pocket guns.

I would shoot it for a while before changing anything. You might forget about its cosmetic imperfections while your admiring its tight groups.