Dug into the clutch today to try and solve the issues it was having with slipping. Was confounded by the special nut locking the basket into the bike, unfortunately, which was evidently overtorqued despite not having any of the finned retaining washer's tabs holding it in place. Using the prescribed hammer and chisel method to tap it loose yielded no results. I'll have to fabricate a socket to pull that before I'm able to access the plates themselves. In the meantime, though, I addressed some other issues...
It seems the cable tensioner at the cover wasn't seating properly and the part that should have been inset and spinning freely in the case was too large-- it rested just a millimeter inside the lip of the hole, and could skew sideways a little. I replaced that piece with a washer with an indent and a nut overtop, and those seem to fill the role alright. That piece may have been causing intermittent adjustment issues.
Springs all measured ~32.35mm, which should be within spec. I noticed that though they were all painted on one end with the same stuff used on the valve springs, half of them had the paint facing in and half facing out. I couldn't find proper orientation listed anywhere, so I took a guess and flipped them all so the paint was uniformly to the outside of the bike (as with the valve springs).
The outermost cork plate had a fair amount of old oil residue on the exposed (long, squared) tabs, so I figure there may be deposition throughout the pack which could contribute to slipping. I squirted some seafoam over the plates, and added some to the oil tank-- hopefully that will clean them up some until I can pull the clutch all the way apart.
Everything went back together fine, and the action at the lever felt a little kinder. Clutch sounded a little noisier when I fired up the bike, but it seems to drop into 1st gear easier with more slack in the cable. We'll see tomorrow if it's still slipping at high RPMs!
1975 CB750F
1986 CN250
2005 KLR650
