Removal of the inner gearbox cover on a 750 (1972)

Hi all,
I want to inspect the gearbox mainshaft and layshaft,hopefully not to strip it.I have no idea of the internal condition as the bike was purchased as a bike needing recommissioning.I need to take the gearbox inner off to replace the trunnion roller,which does show signs of chipping.My question is,do I need to disturb the mainshaft securing nut to take this cover off.I want to disturb as little as possible,and to just visually check the internals.I realise this has been covered before but I cant find a definitive answer on whether the nut on the mainshaft really needs removing.

Yes the nut which is behind the clutch operating mechanism need to be undone, anything more than inspection will require the removal of the clutch from the main shaft.

Just to clarify, you can remove all of the gearbox internals except the sleeve gear, main shaft and associated bearing without removing the clutch, drive chain or gearbox shell from the cradle.