To get the handle sleeve off the barrel, you first remove the screw holding the handle assembly onto the sleeve, and remove the handle. Then you punch through the uppermost little pin (which is covered by the handle base when it is installed). Note that as you withdraw your pin punch, there is a little cap (by the book name: plug) and spring that are going to fly, usually never to be found again. Be ready for this and have a rag blocking it's exit.
With the spring and cap gone, you hold the handle upside down and the lower plunger will back out enough that you can slip the sleeve off. On an early sleeve, there is a second pin retaining the plunger in the sleeve. In a later sleeve, there is no second pin....the plunger should just fall out once you have the upper pin, cap and spring (and 60 year old grease) out.
The fun will come as you try and re-assemble the plunger, spring and cap. You will know what I mean when you try it.