When I rebuilt a pair of vintage Marzocchis I used hose clamps to compress the springs. Crank up the preload, tighten the hose clamps, and release the preload.
if you look at the springs on your vintage marzocchi and the spring on a monster you'll see the rate is massively different.
i'd be willing to watch you try to remove it with hose clamps from a safe distance, but i wouldn't recommend that method to someone else who might actually try it.
