How clean does the block have to be before reinstalling heads?

[bondsman]

In the middle of doing head gaskets. Started cleaning the block where the old head gaskets were. I have been using a razor blade and carb cleaner for the most part. Tried these lil reloc rubber bristle wheels and a fine reloc wheel. The fastest thing is the fine mesh reloc wheel. The rubber things don't do too much. I don't like the idea of the scratches that the mesh wheel leaves so I didn't use it but in a small area. I have been scraping it with a long handled razor blade. It is a slow process and I want to speed it up a bit. How clean does the block have to be? Should it be all clean like the same color everywhere, or just the areas where the gasket lays?
I have heard conflicting opinions on the reloc wheels which has made me scared to use them. I would rather err on the side of caution than screw the block up.
Anybody have any pics of what their block looked like before heads where installed?
Surely Ford or any shop that changes head gaskets doesn't spend the amount of time I have on cleaning the mating surface...

[Goose]

i always used a die grinder with a conditioning pad Google Image Result for http://site.unbeatablesale.com/img100/wtd8548.gif

[PGreenSVT]

The block and head mating surfaces have to be clean of any foreign material to seal correctly. I remember something about a spray on gasket remover but I can't remember where. Maybe someone will step in here that knows what I'm talking about.

[bondsman]

I think those are the same things I have. I picked mine up at advance auto. They were in the body repair area. I have the medium grit ones. Maroon. Does the scratches it leaves really matter?

[07stroker]

I took all the gasket residue off with a razor and a little bit of carb cleaner and I haven't had any problems yet.