Taking one to bits is an interesting exercise. Funnily enough, I removed one a few days ago.
They cannot come off the stay without being dismantled first.
First, set up a temporary forestay.
Then if you undo the stay at the bottom and top after tying it to a halyard, you can lower it slowly and walk it out along a wharf that you are tied to. Try not to bend it too much.
There are two 1/4 whitworth screws securing the furler extrusions to the drum. There are also two for the top casting. Undo them ( could be easier said than done due to the corrosion
in the threads, but an impact screwdriver helps).
Remove the forestay from the rigging
screw. You will notice that the stainless retainers for the furling
rope are welded to a nut that threads onto the end of the forestay. If you unwind this, and use a rubber hammer you can tap the drum and it should slide off the extrusion.
The extrusion is made in halves that slot into each other. Some are locked with more screws, some are not. Just slide them all apart and it will come off the stay. Mark them for reassembly before you dismantle.
There are also two screws in the drum. If you undo the screws, the bearing unit will pull out ( the balls will fall out everywhere ).
I had some problems with corroded screws. For the worst ones, I put it in the vyce with a screwdriver bit so the bit could not jump out of the screw slot and turned the bit with a spanner.
When you put it back together, use Loctite or similar.
Hope this makes sense, any queries just ask.