Eastwood makes a radiator paint.
http://www.eastwood.com/ew-radiator-black-paint-gloss-aerosol-12-oz.html

This may not be any help to you but I will tell you anyway. A couple of weeks ago I put a new cam in my engine. It was a bigger cam so I was expecting it to run a little differently but turned out to be quit a bit worse. I could not get the Idle below 1100 and when I increase the rpm over 3000 it would smooth out but it seemed to be lacking power. I checked everything and could not find anything wrong. finally when I went to pull the plugs I found that the plug cables on 7 and 8 were on but not all the way. I think they were firing but not all the time. Plugged the cables all the way on and everything was fine. My point is that it might be electrical.

Michael

Jay I am reading your book and it is very good and timely sense I have my engine torn down and making some changes to it. I have a number of questions I would like to ask but I think I will just ask one for now.
When I first got my 65 CO 427 it came with what I thought was a Med Riser manifold but there no markings to prove it, So when I saw the picture in your book of it I dug mine out for comparison. It looks the same but there are some things that are differant.
  The date marking of 12-64 above the thermostat housing
  Fewer vacuum bosses
  No bosses for a throttle linkage
The ports had not been touched and I was surprised as to how restricted some of them were. I did some gasket matching but was not to aggressive. I am going to try to send some photos so tell me what you think

Michael Mason