The sandcast 750 had no holes in the clutch hubs, unless a later hub (from a K0) was installed after the first one got gouged up (from the plates not releasing very well). In our shop (Brown's Sport Center, Peoria, IL circa 1970) we received notice(s) from Honda to add some holes, but were reluctant to do so at first (not understanding the problem at the time). After the first one (which belonged to Jim, our lead wrench and the first sandcast 750 sold in Peoria) had been done and the clutch worked [much] better, we started adding the holes.
Every now and then, I have seen a hub come though my hands that is lacking the holes. The splines are usually banged up (not unlike yours) from the clutch not releasing well, nor quickly, forcing slow shifting and sometimes resulting in twisted splines on the shifter shaft from heavy pushing-lifting forces to make it shift. These are often seen on the sandcast shift arms, if they weren't replaced under warranty (many were) from working the shift arm loose from sticky shifting.
Starting in the late New Factory K1 engines, the hole in the center of the mainshaft that delivers oil to the clutch hub grew bigger. Through the [unofficial at that time] "shop rep network" we received word that making this hole a little larger also helped improve the shifting, especially in heavy city traffic. By the K2 model the hole reached its nominal size and didn't change anymore after that.
When I get an early 750 engine for rebuild I drill the oil delivery hole in the mainshaft larger and add holes in the clutch inner hub (2 behind each spline, one in the center of the web, and another in the web) so the owner will have a smoother clutch, especially since modern oils lack any zinc at all, making the plates tend to stick together more.
I think if you search for "clutch hub holes" you'll find many posts here from others who have also done these mods.
