I have both the 350 and 400, as you say the clutch operation is different but as mainframes are the same, I can’t see why you can’t couple the cable in the normal way- you might have a problem with cable lengths though. The 400 clutch cover doesn’t fit the 350 cases but you don’t need to change any of that. The gearchange is different and 6 speed on the 400. Not near my bikes till tomorrow but I have a feeling the 350 lever works t’other way - I’ll check. As the stroke length is the same on both and only the bores are different, I would guess that the pipes would fit without drama.
Can’t think of any other problems you might meet.
Ian
Just spotted that was post 333 for me - spooky, that’s the model number of the CB350F - Off to buy a lottery ticket🤓