My JDM 1L K11 had no tacho wire either. Used a friends JDM 1L K11 as an example & traced the wire from the cluster to computer, then added it to my car, it's only the 1 wire that was missing. Out of three JDM 1L K11 that I know about fitting the rev counter cluster into, mine was the only one missing the tacho wire from the loom.
I have solved all issues with my fuel gauge too. It may have just been the cluster I got having been fiddled with in the past. Anyway, I pulled the needle off & repositioned it. Fuel gauge now reads all the way, full to empty.
I had made a comparision between the fuel gauge meter mechanism & surrounding components. While looking identical, they had different resistances, & the four "poles" connecting to the meter coils were connected differently, in such a way as to make them non-interchangeable. The surrounding components had different values too, one by maybe by around 50%.
From what I gather, nissan tank senders of similar year all work roughly the same, world wide, i.e. 4-8 ohm when full, 78-96 ohm when full. So there should be no real issues swapping between UK-JDM.
As for how common they are, from what I recall, regardless of model designation, every JDM 1.3L has one & every 1L does not. Being Japan, 90%+ of them are automatic, so the speedo has the PRND21 indicator. Thankfully the speedo is interchangeable from the non rev counter cluster.