Yes you can. When I built one of my 9mm AR SBR's I had a complete rifle that I could (and did) use until my forms came back. As soon as that happened, I sent the barrel out to be cut to 5.25" and threaded.
While you're surfing the 'web, you might check out
www.ingunowners.com. We're a local (Indiana) gun forum and there's lots of good local info there.