Worth having a good look around here before you start Paul. It’s important to avoid the points cam falling out when you remove the cover, generally by tapping it in as the cover comes off. Instructions in the Paul Friday download. There may be a write up on the clutch removal. My friend Tonya made a compression tool using threaded rod screwed into a couple of the casing holes, with a bit of bar fitted over those and a “something” that pressed on the outer cover to get the circlip out.
Make sure you use classic oil without friction modifiers. If a previous owner had used that the clutch will slip. Millers do a classic Mini Oil 20W-50 that’s designed for wet clutches and has zinc for the flat tappets. I use Halfords own, but it’s suddenly rocketed in price, and Millers is actually cheaper from Halfords than their own oil (which I think may be Comma).
If you have plenty of friction material left, it’s possibly oil contamination, and a wash in petrol or the dishwasher
followed by the “right” oil may sort it.
One of mine has had a slipping clutch for a while, so I am on the same route as you. I was in Mandello back in July and got a set of plates from Valpolini.
Finally, one of our guys, Martin Nokes, sells an amateur workshop manual which is useful. Often on eBay, or search our Facebook group.
Good luck and Merry Christmas 🎄