I've heard of people using bbq paint and stuff and I used some stuff from auto zone for mine. Don't remember the name and dont have the can anymore. But the cooling efficiency hasn't been compromised. So you should be fine.
Just look for Duplicolor High Heat engine paint. There are two heat ranges(500* & 1200*) both of which are higher than that eastwood brand. Any autoparts store, walmart etc will have it. Just make sure that you prep it by cleaning it real good and give a light scuff prior to painting for adhesion. Allow proper drying time in between coats and don't go overboard laying it on trying to cover it all at once. Don't rush the process and it will last and look good. http://www.duplicolor.com/products/enginePaint/
http://www.tcpglobal.com/spraypaintdepot/DC-engine.aspx
scuff the shiny IC.. you are not sanding it, then make sure to clean the IC properly and spray nice light coats if high heat. no primer involved you are not painting a valve cover you are just covering the aluminum IC enough to make it black with a few light coats. heavy coats will cause the fins to lose some efficiency, you need a few light coats.
i used a 3m red scuff pad to prep mine and not sandpaper.
so the red 3m scuff pad from canadiantire is the one you talking about? linked below is it this thing?
http://www.canadiantire.ca/AST/brow.../PRD~0475778P/3M+Body+Scuff+Pad.jsp?locale=en
will the high engine paint decrease efficiency compared to the radiator paint?