Sure, you could do that. I've qot sketches somewhere of a Quad-T-Copter. I think you could do something where... ok, make it an X-quad-Octo copter (as opposed to a plus-quad-Octo). Space the motors such that you have 40% overlap on each pair, but no overlap between the arms. Then, put the two motors directly in front of the camera "up". So it would leave a "tunnel" of sorts that the camera could look out of. I dunno. It's would have to be sketched out.
Also, it wouldn't be as compact as an overlapping Octo.
As for spacers, I'm planning on buying 40mm screws with 30mm aluminum standoffs. The spacers won't move.
Alternatively, I have though about cutting 30mm sections of heavy wall aluminum tube. then drilling it axially for each screw. No way that would move. The only issue here (besides weight obviously) is that the bolt pattern isn't round, it's more like a parallelogram. So the tube would have to be really thick, or a complicated elipsoid machining. It would be trivial to do on a CNC, But I don't have one.