I assumed there was no inner barrel and all the brass we can see was just a one piece and the front piece just screwed into this.
Looking at the interior finish, it could be the barrel and sleeve have been turned in relation to the various cut out holes for the rack and pinion mechanism and then soldered together.
Yes, there is only one piece. Although it does appear that the front piece use to screw into the barrel, but it too has been soldered in place.
In re-reading these posts and comparing your lens to mine, I would agree with Steve and yourself that my lens has had the original sleeve barrel removed, the rack in pinion hole patched and the mechanism removed. I believe it was designed with only the one lens, but someone altered its original design to its present configuration, i.e., a Darlot pillbox which has had its original sleeve and focusing mechanism removed.