BL I have come across chain wheels where the studs have a narrow spiral flute at the none threaded base end, and are simply "nailed" into the chain wheel rim from the rear. You might find cutting the bad ones flat will enable them to be simply knocked out. Support the rim to prevent distortion. If yours are brazed, soften the braze with heat and push them out.
The threads are 2BA. I made my own nuts, tapping a thread in a hex bar, then parting each one off in the lathe with a small cutaway to clear the raised rim of the cover, just like the originals, they looked better than new.
The cover is not essential, as long as the oil level just kisses the chain, no higher, the plates will remain reasonably dry, but the cover also adds rigidity to the clutch basket. Even held on with a few Loctited nuts is OK, you won't notice any imbalance compared with the rest of what goes on within those crank cases. If a clutch adjusting nut loosens, you will hear it grinding the clutch cover rather than the primary cover before it drops off to do major damage.
Swarfy.
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