Black Sheep
As duTch says, the drive spline ring comes off after knocking back the tabs, undo the nuts and remove the 6 bolts and it should drop off. Centre circlip should have a thin sheet steel grease retainer, described as a bearing shim, between it and the bearing. Depending how you want to treat the bearing, warm everything up and it should come out easily with a draw bolt and washers or a big hammer. Smacking a centre race, unsupported in this way is not good for bearings, but you knew this already. You may also have to swap over the other "collar", the ring that keeps the grease in on the inside, backplate side of the drum. This will knock out with a bit of care. Put a dab of loctite on it when you replace it in the new sprocket drum. This assumes you have the right sprocket, made to original dimensions.
Swarfy