yes, check out autometer.com and they have info on what color wire to tap into. I assume you have a tach, so what you do in run the tach pick up wire to the distributer (where all the spark plugs are) and there is a couple of wires going in the distributor, one of those is the one you need to carefully tap into. It will vary based on year and model.
yes
Since the coil is in the distributor, simply hook the tach 'trigger' wire to the out put on the side of the distributor cap marked 'tach'.
Yea, a 300ZX's engine can fit into a 240SX although there might be some need for adjustments in the engine bay.
It should work. I have a 94 w/o a tach and put a LE version cluster with tach in. Works fine. There should still be a tach wire grouped into the harness plugs. Just unplug your old one and plug in the new one that's it.
Yes
the red one
there will be a spot on back of distributor cap it will say tach run wire from there to gauge. You probably need to run a switched 12v lead as well to illuminate the tach at night. The tach slot on the distributor will take care of 'timing' the pulse to the tach. Often times the tach will have a switch setting for 4-6-8 cylinder. Read the manufacturer instructions carefully.
Yes you can no problem.
RB26DETT N1(Comes off a GTR R34)
$2000
um parts + labor... parts can be found on eBay and labor well, depends on where you live call a mechanic - it cost me 1100 to put one in my 90 240sx
You would always want to have your tach in a very easy to see place. I have seen many mounted on the left window molding. They do make a gauge mount that replaces the original factory molding.