Here is a diagram with old-style part numbers, and a set of instructions from Alf Briggs in the 1960s. Apparently, Alf was Honda's first English (or maybe European) employee and he looked after all the race bike parts for the CR93 and other CRs.
This is the instruction set for assembling a 5-speeder. The last point is particularly interesting and appears to describe the later style clutch hub and why it was introduced.
Here is the clutch hub with that central boss....
And here is how the oil gets out of the pressure plate to keep the oil away from the plates. The original designs were obviously directing too much oil into the clutch pack and causing slippage. This was a neat way to get less lube in and more friction out of the existing clutch pack.....
G