Rattle can will work fine as long as its properly prepped.
Black color is 60 degree black..... Eastwood sells the black under hood paint, its a satin finish. Engine color: medium blue metallic.
NAPA also sells the under hood black its made by Martin Senor paint.
Duplicolor's medium blue is a ice color, NAPA sells it. That color is hard to find at say AutoZone.
Use an etching primer on bare metal
Before I removed the motor and painted it with a compressor, I used the duplicolor medium blue metallic.... the picture provided is the motor rattle caned with duplicolor's med blue met. I painted it with it in the car. Covered everything. Used a lot of brake cleaner and degreaser. Took some time but it held up a few years before I restored it.