Brian,
This has been a subject of much discussion, with a variety of colors being found on original engines. But my 58 235 was originally blue, and I have kept the same color scheme. I know there are suppliers of the paint out there, and I believe Jim Carter's carries it in their catalog. For the minor repaint work I have done so far, I can tell you that the Dupli-Color engine enamel in General Motors Blue (DE1608) was a close match to the surviving paint on my block.
But at the end of the day, I gotta hold with tclederman...paint it whatever color you like. And the blue ain't bad.
