Originally Posted by JonL

Gotta take issue with a few things in this post.
1. A sheet of paper is probably too thick to use to check for a warped head. It also isn't rigid and flat enough to reliably pass under the straightedge. You need a REAL straightedge (a machinist's straightedge) and you are checking for flatness of around .002" (depends on the manufacturer's specification). Use feeler gauges.

A piece of notebook paper is .004 to .006 thick. Its what I used and it worked fine for me. No leaks or issues with the gasket seating correctly. Are you saying anything greater than .002, one should have the head resurfaced? While I don't know what the MB spec is I'd think it is more than. 002.

2. Do NOT use wire wheels to clean any flat aluminum surfaces!!! I cannot emphasize this enough! The wire wheels will remove aluminum and DESTROY the sealing surface. Even on an iron block you should use care with a wire wheel.

Once again, I used a wire wheel on mine with a hand drill and it turnd out fine. No scratches on the head's surface or anything. Just a finely cleaned surface. You surely can use it safely on a iron block.

3. Careful use of a tap is fine for cleaning up threads in a block. (You wouldn't be cleaning head bolt hole threads in a head.) In fact careful use of a tap would damage the threads less and remove the junk better than a wire brush, although a wire brush might be "OK." If you use a wire brush you have to be sure no stray bits of brushes (pieces of wire) are left behind.

I used the wire brushes because I didn't have a tap and die set. And again, this method worked fine for me. I was careful to clean out all holes with a magnetic tip pointer.

I would only recommend something that I know would work and has worked for me.