Exhaust Manifold gasket residue removal

I have removed the exhaust manifold on my 1988 GW. I want to clean up the gasket surfaces on the manifold and engine. I was told to sand off the residue with a 3M Automotive Sanding Sponge. I tried it. If I had 100 years maybe it would work. Right now I am trying Permatex Gasket Remover Spray(765-1230). It is supposed to loosen the residue in about 10/15 minutes. No such luck, I keep reapplying and scraping with a putty knife but not much is happening. Can anyone give me an idea on removing what appears to be a black coating on the mating surfaces of the manifold. The 3M sanding sponge works so slowly that it is not a viable option.  

Thank you for any ideas.
John  

mabey a wire wheel and a die grinder  
"WHEN IN DOUBT TACH IT OUT!"

a razorblade will do it