I've got a 95 Bluebird LX (U13 series 2) and this is how i did it:
The back 2 speakers are 6 inches and took a while to get to. You gotta unbolt the back seat, do the bottom first and follow with the top part. Note there are 2 bolts behind the middle armrest you gotta undo first, and i think some of those 'pop plugs' on the sides, it should lift out then pretty easily. Take out the back brake light and disconnect the wire. Then slip out the whole parcel rack and you should be able to get to the speakers pretty easily. Unscrew them, cut off the old wires, splice/solder them to the new speakers and drop them in. Screw it all in and put everything back together.
The front speakers are 5 x 7 inch, so make sure you don't get 6 inch or 6x9 speakers. The front doors both have the 'pop plugs' around the sides and bolts at the bottom of the door. The passenger door has an extra couple bolts: underneath the armrest and beneath the electric window button. So pop out the cover underneath the armrest and pop out the electric window button with a screwdriver, undo the screws inside and don't forget to take off the little trim dish around the door handles, it should come out pretty easy. The driver's door also has a bolt in the other dish in the door that has to be undone too. Once the door is off disconnect the wires from the windows on each and you should be able to get to the speakers quite easy. Do the same as above now.
Check that your 5 x 7's will fit though because i had to trim all the excess metal around my speakers and wedge them in the stock speaker brackets. Then i drilled some new holes into the metal and screwed them in pretty solidly.
I think there are a few trouble's with the head unit too. I already had an aftermarket head deck though anyway when I bought it so it wasn't too bad for me. Still had to take nearly all the panels off inside: the one surrounding the gear knob (the gear knob just twists off too), the panels under the steering wheel and the actual housing around the deck. There is a bolt that is under the steering wheel to the left that needs to be undone to get the housing around the deck off too. The panels under the steering wheel have to come off, take off the fuse panel first and also the 2 bolts at the bottom left and right of the panel too. Then i unsrewed the original deck and put the new one in. Then just match up the old wires to the new one after cutting them off from the old deck and splice/solder them on. Then put it all back together and see how it goes. The jbl 5x7's are actually surprisingly good, a guy at strathfield said he put 4 of them in his mates 180 and they pump.
Now putting in the sub wasn't too bad. It's all pretty straightforward. Just clip off a little hole in the battery cover on the positive side for the power cable to run off, attach the fuse to the air filter with some double sided tape and go through the gromet on the right side corner of the engine bay. Just feed some wire through until you can eventually grab it on the other side. Note you'll have to take out the side panels along the left hand side of the car and also lift out the mat covering the front passenger seat under the glovebox to get the wires. Then just feed it all the way into the back and finally into the boot (It's pretty self explanatory) and connect it all up. I used a little bolt beneath the boot mat to attach my ground wire too.
Hopefully this helps someone cos there is nothing about nissan bluebird sound installs on the net that I could find. Good luck
