Thanks both for replies, information and for the compliments about the bass. I absolutely love it.
What seemed interesting is that looking at other basses supplied to Rothchild around that time, it looks like a few have the channel bridge, so I wondered whether that was something they had specified. However, I agree that this is most likely a modification (tailpiece at least) done by one of the owners.
Either way, everything works fine and it performs beautifully. Personally, I would prefer the newer tailpiece and I will think about changing it at some point if the current one isn't original. It is a bit oversized.
I just had a re-fret done (in the UK) because I didn't like the feel of the frets and some were a quite worn on closer inspection and more playing time. It had been re-fretted at some point, and not very nicely. So, I had slightly larger Jescar Gold frets fitted because the colour seemed to suit the look of the bass, and indeed they are great.