You have a couple of options.
1: If the car has a clear coat on it, you can wash it to get skin oils & other contaminants off, then paint it. The clear coat will act as a primer, and the paint will stick to it.
2: You can strip it by soaking in lacquer thinner and cleaning the clear coat off, then etch the car in vinegar. Wash, dry, and paint.
3: Know anyone with a blasting booth? I blast the models, ultrasonically clean them, then paint, but this is the most expensive way, as it requires the most equipment.
All methods will work...I didn't always have the blasting booth or the ultrasonic cleaner

Also, I would very strongly recommend Scalecoat 1, not Floquil. Scalecoat 1 is formulated for brass, and once baked on, gives you a gloss finish good for decals without having to clear coat. You can dullcote after decaling.