Hi, foxfire,
Disassembly is the easy part, as the gun is sort of a break top version of the Rast-Gasser. Many have been mutilated by attempts at disassembly because the owner did not know how to do it.
Simply put your thumb on the checkered space at the rear of the trigger guard, press forward and down to unlock the guard, then swing it down. Insert the thumbnail in the notch above the front of the trigger guard and swing the sideplate outward on its hinge in the top of the grip. From there, all internal parts are accessible and can be removed, though I don't recommend removing the right grip or the extractor cam. The cylinder removes simply by lifting the latch and pulling the cylinder while rotating it to the left (counterclockwise as seen from the rear).
The Type 26 refers to the adoption date, the 26th year of the Meiji reign (1893), but actually the gun was adopted in 1894. I don't know why the difference, except that the final design was done in 1893.
The 9mm rimmed cartridge is strictly Japanese, though many owners have shot .38 S&W by trimming the rim from the front and running the round into a .38 Special die. The revolver is adequately sturdy for a break top, but original Japanese ammo in tests showed a muzzle velocity of only about 500 feet per second.
The early guns were a beautiful black charcoal blue, equal to anything Colt ever made. Later guns are rust blued, and also very nicely done. Some were later rebuilt with mixed parts, with or without refinishing.
Some late ones have wooden grips grooved horizontally, sort of like the German P.38 plastic grips. These may just be replacements. Total production was about 60,000 guns. Assembly numbers and also code numbers were used in addition to the serial number and will match on an original gun.
While records are sketchy, original production probably ceased in 1928, although guns were built from parts, rebuilt, refinished and reissued into WWII, by which time it was substitute standard.
There are two holster types, both uncommon, a leather holster and a canvas holster. Some French Mle. 1892 Lebel leather holsters have been sold as Type 26 holsters, at a much higher price than the more common Lebel holster. (One fellow was a bit unhappy when I told him the French name written in his rather salty "Type 26" holster was not due to its capture by a Frenchman.)
Collectors break the guns down by periods based on serial number and finish type, but I don't know of any breakdown by production date.
While I have two Type 26 revolvers, most of the above was taken from The Hand Cannons of Imperial Japan, by Harry Derby, a book I very much recommend if you can find it.
HTH
Jim