I would think it's a conversion done by someone. I don't think they usually stamp the weight on 2 piece cues although I could be totally off by assuming that.
Doesn't look like old Brunswick to me. I've never seen a Brunswick butt lable that looked like that. I'm assuming that part of the joint is missing on this cue, otherwise it doesn't look like the shaft and butt would fit together. If that pin is coming out of the shaft, it's definitely old, but that's about all I can tell given the pics.
You're right on that, the central Joint collar is missing, possibly SS or Brass?
As reguards what brand/model, I'm not sure, but I thought it was a brunswick too, untill Mr Hoppe had mentioned the logo plate, and so, I'm now wondering id it may be a dufferrin conversion??