Well, based on that label this saw was manufactured in June of 1999, one of the last ones before the MS260 came out. The carb is likely original.
However, the screw grommet still looks wrong. Looks like someone trimmed the wrong one and jammed it in there. The function of the carb screw grommets is to guide the adjusting screwdriver and seal the carb enclosure to keep dust out. I will attach some photos of how one fits in a MS260. Notice the screw guidance and the tight sealing with the carb box. BTW, the grommets for the 260 and 026 are NOT interchangeable as the tank housings changed with the model update.
The A/F cover with the round knob is definitely the old style but I think it may have been required for the old narrow filter. If you update the air filter / carb you might also have to update the A/F cover. The issue is the latch mechanism that holds the A/F cover on. Someone else may know for sure. I have never really messed with the old non-pro 026's and this is one of the reasons. The other is the non-adjustable engine (NOT chain) driven oiler.
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