Dont rattle can it, When it rains the water will leak through and rust will eat the body from the inside. Heres how you do a good fl;at black paint job, it aint easy.-
Take the car to have it soda blasted, it wont cost much and it will completely strip it clean. You the need to do all the filling and body work which will include some bondo, block sanding guide coat and possibly some panel repair or nonlead solder filling for a straight body, You need to go the whole nine yards because if you do not it will look horrible and any rust will continue to grow and flat black shows every little detail. Im not talking barret jackson snob horrible Im talk a little kid comes by and asks why your car looks so .... up. In order to get the proper look of flat black you will need to do a few custom touches- Shave the front marker/turn indicators minimum and I would also shave the rear trunk lock and fab a switch in the cockpit like new cars have. Primer with gray and then spray with either John deer blitz black or dupli-color DP-90 and cover with a matee clear- YOU HAVE TO USE THE CLEAR!!!!! Water will soak through the primer and you will begin to see rust through if you do not- I KNOW FROM EXPIERINCE!!!!! It will not take long for that rust to become cance with no protection. Flat black only looks kool when done properly, you cannot trust picture because no matter how high quality It dosent show conditions in deffernt light or the details. Its ok to go cheap, but its never ok to go lazy!!!!