Gew 98 rear sight question

I recently picked up a cut down DWM G98 dated 1917. It has had it's barrel cut to 23-3/4", stock badly butchered and the receiver drilled and tapped for a receiver sight so it's too far gone to restore, which is sad since all the numbers match. However, it has turned out to be very accurate (8x57mm) so I now find myself in the midst of a sporter project. I have bought a euro style semi-finished sporter stock and am about to fit it to the rifle. However, I have a question about the rear sight base. (See PICs). When I got the rifle, the original rear sight had been removed and what looks like a sight base left on the barrel. I have made up a collage showing the sight base (three views) and the stock inletting. Is the base machined integral with the barrel or is it a removable sleeve? Looking at it closely, I really can't tell. If it is a sleeve, How do I get it off? Should I just leave it on and fit the stock to suit?
I don't want to start taking wood out of the stock until I know what I'm doing here.
https://www.milsurps.com/images/impo...scollage-1.jpg

Thanks in advance for any help offered.

It sure looks like someone turned down the rear sight base. The base is actually still there. But turned down on a mill. Lots of work. Base is put on with lead soldier and very tough. Odd, to say the least.