ATI does not have a part# for a 9" barrel for the lite weight, even though they
do sell a LW pistol.
i'm still waiting on a reply from them. progress documented in
this thread.
you could cut/re-crown the barrel. that would be around $150-$200, as far as i know.
are you concerned about the reliability of the plastic receiver in general, or in SBR form?
i'm thinking if it's good for 16" barrel, it should be as good, if not better, for 9".