The correct flow of power through the drive train is

• engine - driveshafts - clutch - mainshaft - countershaft - final driven gear - wheels
• engine - clutch - mainshaft - countershaft - final driven gear - driveshafts - wheels
• engine - clutch - countershaft - mainshaft - final driven gear - driveshafts - wheels
• engine - mainshaft - countershaft - clutch - final driven gear - driveshafts - wheels