We've strayed from the topic of exhaust, so I might as well add this photo of my 1965 C10 factory bell. This is the blue I was trying to match. I bought high temp paint from Eastwood that was supposed to be correct . . . and then you open the can and scratch your head and hope it matches better after it dries.
I am happy with the color. 
My '78 bell housing on my Sag 3spd has overspray blue on it too. I guess the clutch and bell housing was assembled with the engine prior to painting on the line. They didn't seem to bother to paint the whole bell housing, just get all the cast iron covered and paint on the bell housing just seems inadvertent.
