I installed the clutch basket on the lathe and just did a simple "boring" operation. The FCC basket had a clearance of about 0.5mm with the backplate, so this was not really a critical job and it was easy to aim for a tighter clearance as well.
I didn't bother with making or buying new rivets as well. I just used a tap to thread the existing holes. Just out of memory, I believe it was a M5 tap that I used.
And here is the end result, temporarily fitted on the bike and everything looks good.
Keep in mind that the wet clutch pressure plate can also be used for the dry clutch as well.
Have fun and keep the two strokes alive.