OK, so after no real responses, I'll give this a go.
The plunger dust cover 'sleeve part' that sits over the hub is so much longer, than on a swing arm dust cover, so trying to just exert some pressure on the disc will not suffice to remove it.
"The only way to remove it is".
DO NOT LEVER ANYTHING at all, you will Fu:CK IT UP.
Really clean the whole thing well, so as to find the spot welds.
Once you have found the spot welds, carefully drill them out. If you drill through both plates it wont be too much to worry about.
Then cautiously lever, 'separate' the cover plate away from the sleeve part.
Then with a bit of careful heat and leverage you can get the 'inner sleeve ' part off the hub. There is no thread, only a very very snug fit
You will of course need to weld the two parts back together though, and if there was some nice drilling work, followed by a bit of nice welding, and a bit of sanding, the end result should be sweet.
Bang it back on carefully.
Hope this helps a few
Cheers Thomas
Thanks Swarfy, I did see your reply, a bit late though. Cheers