I have read the 3M White Bristle Disc is the go to for cleaning aluminum heads without damaging the surface so I am going to give them a try. They would also work on the cast iron block I'm sure. I will post results.

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Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT