On closer inspection using your photo (as I hadn't compared it to the actual parts that broke) it is the rear end of the cylinder itself that has sheared off.
Interestingly enough though my internal sleeve is slightly different. In the image there is a two part sleeve that surrounds the last 1/3 of the cylinder shaft and in the photo it each half lies flat. Mine is a one piece aluminum sleeved. Nonetheless it is the same handle ad lock.
That picture is just one I linked to that is in the tech tip I also linked to for identification here on the Stovebolt. Having discovered how many changes GM made between Chev's/GMC's, and Canadian/American trucks in those days, I'm not surprised your parts are different.
