I am in the middle of a head gasket job and wanted to get input on how clean to make the pistons. The attached picture is after scrubbing with a scotch-brite pad and using brake cleaner. Is this good enough or do I need to put more effort into cleaning them up? That carbon is hard to get off.

 

That looks fine. The idea is to remove carbon buildup, that could could get red hot and cause fuel to ignite prematurely.

 

Also,

Rotate the crank so the piston you are cleaning is at the top. That way you don't scratch up the cylinder hone and minimal debris gets into the rings.