Yes, it separates there. If you take the back wheel off and undo the header at the cylinder head you can fish the whole assemby toward the rear of the bike so it will be easier to work on.
Tap it all around lightly with a rubber mallet until it loosens up. Lube, twist and sweet talk it til it comes off. When you reinstall it clean all the rust off, give it a coat of paint and NevrSieze the inside of the joint.