Need to split the casings to change primary?

Hello again people,

After reading around i seem to have an idea about what is needed to change the primary drive on this smallframe. But i wanna make sure of one thing, is it true that to change over the clutch and crank end gear which make up the primary drive that i dont have to split the crankcases but merely need to remove the clutch cover?

Sorry i know i am an ignoramus but i simply dont understand what exactly is needed to change the primary drive, could one of you guys please humor me and go through it for me? On a largeframe it is quite a simple process but from what i can tell from smallframe diagrams there seems to be another link in the gearing that i dont quite get yet

Thanks boys much appreciated

you will have 2 split the casings as the clutch bell is held inside the engine by a circlip