I painted my engine with that paint and I didnt used any primer(some guys do), Just clean the parts leaving no oil, rust or dirt using a wire brush if necessary, then spray the paint and let it dry until the next coat. Well, thats the way I do it.
I used it on my 500 Cadillac, the engine was completely torn down so yes, I first cleaned it so you could eat off of it then primed it with Duplicolor 500 degree primer. I then used the top coat and ended up putting 3 coats on, not a show job......but it's an engine after all. Preperation is very important, you do a chitty prep job and you get a chitty paint job that won't last.