What is the difference between this model Clutch Drum and Clutch Drum part #4140-160-2909? Will either model fit a 2007 production Stihl FS55 brush cutter?

I have checked this for you and I can see that the correct one for your machine is: https://www.lsengineers.co.uk/catalog/product/view/id/17722 This is the only one listed for the FS55 on Stihl's website. The one you are looking at is for the Kombi machines.