My take on this is it's a quite modified guitar, the obvious being the pickups mounted into what looks like an original carved top acoustic instrument, which of course a Blackstone was (hopefully they are floating as you suggest because the photo's look suspiciously inset into the top). 1949 is acknowledged as the end of that line, so that is fine, and it would have had the push type truss rod adjusted from below the fretboard extension, which if it works is fine (mine does) and if it doesn't it becomes non-adjustable (and still kinda works). The short rod you have is the remains of the now-removed original truss rod. The Gibson style rod you have now was a retro-fit. On an instrument like that, originality is now a moot point, so if the neck is bowed to need a truss rod you can take the fretboard off and install one, you or someone else depending on skills. The damage is already done, now you can simply make it good. Good luck!
As an aside, on my Zephyr the neck joint failed and the fretboard extension got perilously close to the top, such that the truss rod adjuster just about touched the top, you might find a little scar there about an inch from the end of the fretboard under the extension.
http://wiedler.ch/nyepireg/models.html#ArchtopAc The headstock logo looks correct for post 1947 Blackstocks, per this anyway. In fact aside from the obvious the whole guitar looks quite correct, good find in my opinion!