What is the correct way to clean the top of the engine block when changing the head gasket?

I usually carefully use a gasket scraper and some carb cleaner or something.

You have to be sure the bolt, water jacket and the cylinder holes do not accumulate crap from the scraping. The bolt holes are easy as compressed air will clean them out. Judicious use of tape will cover the others. When you are ready to bolt down the heads, use brakleen or similar product to clean the bolt holes. Bolt holes need to be absolutely clean. It is also a very good idea to use new bolts and to chase the bolt holes with a bottom tap before the final air blow out. The final scrape of the head and the block really works well if you use a simple single edge razor blase scraper with light pressure.

I use the flat side of a bench grinder wheel with the paper label removed. Spray the block surface with carb cleaner, and rub back and forth with the grinder wheel. It removes all the old gasket material down to the metal, while maintaining flatness. Be sure to thoroughly clean out the head bolt holes with a tap, then carb spray, then compressed air. Many head gasket failures are due to oil or antifreeze remaining in the bottom of the bolt holes, causing the head bolts to hydro-lock and not getting tight, even with correct torque wrench reading.

Buffer wheel with rubber pad, or I use a scraper and some gasket remover and make sure to block off all orifices.

For the bolt holes, use brake clean with a shop vac to suck the liquid out. Rinse and repeat.

Dead on for you and 4runna. Just need to pay attention to where the crud goes. If it gets into the water jacket, maybe no prob with a good flush. If it gets into the cylinder piston-wall gap, that can be a real problem. that's why I suggested sealing both as best as possible. Then vacuum like crazy. Cleanliness is next to Godliness........

does anyone ever use a little never-seize lube on the head bolts ??? I doing a motor rebuild and using new headbolts and everything is really clean, thanks !

I've always wondered if that's a good idea. I've wondered if the never-seize will break down with the extreme heat/force in there.
My bigger concern, though, is how having it on the threads (and getting kind of squeezed around when you're threading them in) affects the torque reading when torqing down the head bolts, it probably won't be "true".

I'd bet EB has the answer...

Whoa...that's gonna be a BIG NEGATORY on any creative condiments on OEM head bolts. Anti-seize is great stuff when used in the right application, and this most certainly ain't it. You don't want anything that will change the friction when torquing head bolts. Note the torque differences using ARP head studs with their lube vs. oil.

I was pulling my front hubs yesterday, though, and the tiny bit of anti-seize I opted to put on each of the infamous cone washers resulted in the easiest removal ever.