Assuming the saw is original,the black tag should make it an xp. Also had silver tags for se/xp.Transition to xp was around 1986.There was never a plain 266 even though the tag says so. Either SE or XP. To remove all doubt if the carb is a Tillotson s163 it would be a SE. If it has a S224 it would be an XP. They went from SE to XP. Cylinders are the same. Same with intake,etc. The 61,268,272 have many interchangeable parts with it. The 266 is pretty close to a 272. Very good saws.