With the exception of the immediate area surrounding the exhaust port, nothing on your engine should get hot enough to ruin standard Duplicolor paint. On the engines I've done, they've only discolored a little and didn't get hot enough to cook the paint off, but I was only running the bike for 15-20 minutes at a time.
Spray paint won't hold up to spilled gasoline though. If it's had a long time to cure, it's more resistant than fresh paint, but it'll still not as resistant as two component paint sprayed from a gun.
And yes, Dover White is the closest match I've seen to date. I thought about taking a sample of it into a paint shop and having them mix up some in two component, but haven't had time to do much with my bikes recently.