Brake clean, contact cleaner, brown scotch brite and white scotch brite. Brake clean to cut the grime, brown to clean the non polished surfaces and white to clean the polished faces, then contact cleaner to remove any residue off the faces.
If you use gun wash it cuts the grease and doesn't leave a residue. It's used to clean paint guns. I use it when assembling river boats, best thing for pre cleaning welded areas.
I do as above with the brake clean and acetone with scotch bite pad but then I wash off clutch half's in a bucket of warm water and sunlight dish soap rinse and blow dry.
I use brake clean and than wash with hot water and compressed air to dry also use valve lapping compound on pto shaft and install clutch turn 25 times to get rid of the high low spots on the crank to clutch mating, than clean up shaft and clutch mount area with brake clean. fireup and use scotch bright pad at idle with no belt to cleanup faces.