Rebuilding an engine and upgrading the clutch are two separate items. The engine can be rebuilt using the old clutch, drum and gears. Visually you tell the old from the new clutch and drum by the clutch drum. The older drum will have holes in the front face, the newer ones don’t. The gears should be replaced when the new clutch is installed, but the only way to know is to pull the side cover of the engine. Below is the old style clutch.