I use duplicolor 500 degree paint on all my engines without primer. A bead blast should have given a good clean surface with plenty of tooth to stick. Would you be using a 500 degree primer? There are 2 aluminum colors , aluminum and cast aluminum. I am a fan of the second.
This stuff is real easy to run when applied so do light coats( I use a hairdryer to set it and stop possible runs), Then when covered well with light coats, do a uniform overall coat ( continue using hairdryer) .
I use VHT for the pipes , but the flat black doesn't stick or ware as well as other colors.