if you decide to do the gauge cluster swap, do not follow the directions in the sticky. It is way too much work, I have done it in my 90 sentra and it took about 20 minutes my way. What I did was to pull a tach cluster from a car at the junkyard and also the harness from the SMJ (super multiple junction) behind the fuse box, this harness runs behind the gauges and has the plugs for your hazard switch rear defroster etc. It took maybe 15 minutes to remove the cluster and harness, and about 20 minutes to swap the clusters and harnesses. this way their is no cutting harnesses no figuring out which wire goes where and so on, you also do not have to add a resistor as the tach harness and gauges was an option on the B12 sentra's so it will swap right in.
If you want to just add an aftermarket tach I can help with that also as that is what I did in my car before the cluster swap. Pm me if you need help or advice. If you can't find the parts where you live I may be able to assist in that thru my local junkyards as well.