Youll have to scuff the clearcoat. Then if you use POR-15 primer and Black overcoat (Both brush-able self leveling paint if done carefully.) Should look very good. The POR-15 comes in High Gloss, Matt and a Color called cast-iron that's for exhaust manifolds but I've been thinking lately it could have other uses.
Note, this paint goes a LONG LONG ways, a pint would probably do ya... of primer and overcoat. ITs seriously tough, only use it if you NEVER want to take it off.
Don't Open the can, use 2 self tapping large screws, put 1 in the lid at the edge and 1 on the side about 1/4 in blow the rim. If even 1 drop gets on the groove for the lid and you put it back on it will only come off with a can opener. The screws allow you to pour some out replace the screws and when you need more take the screws out and pour, very simple...
Dave