Is magnesium typically cast to final form? I believe that is the case. Wax can be 3D printed so perhaps magnesium parts could be made through a combination of 3D printing and lost wax casting, but it seems a complicated and (prohibitively) expensive way to go about it.
I really don't think cast aluminum would have the strength needed. The parts of want made in aluminum would have to be stamped or forged.
Magnesium is an interesting metal to cast as it likes to burn. As Mercedes found out long ago at La Mans.