Dampening side cover noise.

I used thin corrugated cardboard, glued to the inside of the clutch cover. Then I fitted the side-cover, turned the engine over a couple of times, then removed the cover and cut a circle out of the cardboard where the clutch lugs and Philips screw rotate.
Then I coated the rest of the carboard with clear RTV silicon sealant.
Quietened it down nicely.
Now that I have a shift kit, there's also 1/8" plastic glued to the outside of the clutch cover - even better.

Slightly OT, it's well worth squeezing small blocks of rubber between the fins of the engine and head, too. The difference has to be heard to be believed.
Pic below.

Thanks K.i.p.
Ordinary corrugated cardboard is too thick, but the thin stuff like used for small electronic goods etc is perfect.

The head is from Rock Solid Engines in Australia. Machined billet aluminium, 16:1 compression ratio.

Here's a shot of the cardboard, before the silicon was added.