I found these for several different Ducati flavors with conventional swingarm and hollow rear axle. This is exactly what I want - it seems to me that if I can find something with the same diameter hollow axle (or bigger) and the same axle length (or longer), then it wouldn't be hard to fit them to the 620:
Rear Axle Spool SlidersIf I order something with a larger dia than the 620's axle, then it's a straightforward matter to turn them down on a lathe, and similarly cutting down the rod that runs through the axle isn't that complicated. For me, the real question is how come nobody is making such a project for the bike? Or why can't I find it if they are?