You need to start with an etch primer. There are several available. Make sure you give the alloy a good clean. I know it is clean from the SBlast, but the oxide forms quickly. So give a rub over with a scotchbrite and some detergent to ensure it has no oil
spots contaminating the surface. The etch primer MUST coat the entire surface to ensure a good long lasting bond. I suggest going with an epoxy
system. This can be obtained in both one and two pot systems. Two pot is the harder, but slightly more difficult to apply. Two pot etch primer will need to be used along with two pot undercoats.
pot epoxies and etch primers are available in spray cans. It is still a good wearing product and is much easier to apply.
Or you could send the housing away and have it powder coated.
it results in a good hard wearing finish that will last many years, but when it does eventually fail, it tends to become a real mess.