You can identify the late-model Ironhead Sportster cylinders by the flat cooling fins on the inside near the intake manifold clamps. I'm not exactly sure when they started doing this? Maybe around 1981?
This is my choice of paint for all black, iron H-D cylinders. Clean the spray tip and can after each use. Blow off with air. Lately, the cans have been real finicky - either clogging all together(PJ-1 sent me a new can) but now it leaks out the spray tip and drips. AND, It's expensive. But it looks the best, and stays on.