Its always a bit tricky to decide whether the potential weakness of aluminum outweighs its weight savings.  As a designer one must ask a few relevant questions before deciding.

Has aluminum been used in this case successfully by anyone else?  In this case yes.  Many aluminum stems tap holes straight into the aluminum body.

Is the new part able to hold the same forces specified for the original part?  Haven’t checked yet but this is simply seeing if the nuts can hold the same amount max toque.

What’s the safety factor of the new part compared to the original?  A comprehensive and destructive test can be done to figure this out.

Is this component a critical part that can lead to safety issues? Yes, I’m afraid it is.
 
Picture 5747
Picture 5745
Picture 5741 Picture 5743