Interesting, here are a few random thoughts I get when looking at the photos.
Looking at the yoke, the shape and satin finish remind me of MK14/16, but the stamped S is slightly different and I cannot find a match in just a few minutes of looking. The plastic Scubapro saddles were mostly smooth finish, this one has the textured plastic saddle found on MK5 style first stages sold by Oceanic and perhaps a couple others. The switch from 4 to 5 lp ports was made about 10 years before the switch from flat yoke screws to modern round yoke screws. Aside from the satin finish, the swivel shape is slightly different from other Scubapro MK5 4 lp port swivels The sticker on top of the yoke screw is not at all a common style, but can't recall at the moment the relevance as a clue. I don't think the dust cap is Scubapro version, but those are sometimes replaced so that may not mean much.
Taking a guess and following my intuition, the body could be non Scubapro and the yoke was switched out for a SP version. The fact that is was purchased disassembled does make me think this could me a mix of different brand parts.
Or this could be a very limited edition.
I'm out of time for now, but will be thinking on this. Perhaps we can find a brand that made a satin body version of the MK5 with 4 lp ports which matches.
By the way, could you say what year this was purchased in Barcelona?