Below is a sample of some engines I have built. The Hummer, however, is a diecast model and is prepainted. The two jeeps, though, were painted by me.
I've had the best luck spray painting (usually from a can on 1/24 models, airbrush on my HO scale fire trcuks) gloss red, then finish with either Future or Testors Gloss coat.
I have sprayed gloss over flat/matt finishes in the past, and I just didn't like the final results. It never quite achieved the smooth, glass-like finish that I wanted. This assumes that I did it correctly, and we know what happens when you assume.
There may be some folks out who have had good luck with the flat technique. What you may want to do is go the Painting part of this forum and float your question there.
Good Luck!