If you would like rear brake discs, I can tell you about the mythical Nissan 100Nx SR known in Germany, I have been told that is the only 1.6 with abs. I'v never seen one not in real life or on the internet. I would like to find one for parts since my interrior is gray 1.6 and so it lacks the cover on the abs computer, passenger site at the feet, it looks like there are grey covers around. If there are Nissans 1.6 with abs around it is time to learn what those are and it probably is a bolt on.
Does someone know if hubs from a k12 will fit and might the k12 have abs and or rear braking discs?
But for now, please let me know you are sure you rear drums brake even and with the one click handbrake trick, it is not so one drum is fixated and the otherone is still loose and easily turned by hand. Fixing this will give better results, making sure this is not the problem, then let us think how come rear braking is so much off. Nice brake drums brake just as well as some front discs aslong they have been paired by Nissan.
One question from me, from where do your front callipers come from?
One final thing, if there really is a Nissan 1.6 with abs, it should have rear braking discs but there also should be more Nissans 1.6 with brake discs all around. I wouldn't know how to find those without have a good and preferably long parts source webpage telling where that part fits