Not Sure But?
One way to tell is to pull muffler andtakt a piece of very thin wire or solder and measure bore size, easier to do with plug out also.
A 56mm would be an 1100 which top cover and muffler seem to indicate. I have never seen one with the decomp valve though?
It may also be part of 280,380,480 family as top covers are also about the same ,
I am sure some one here will set us both straight! Nice looking saw though!