I assume you are going for a street performance normally-aspirated engine. I would also recommend upgrading to the JWT valve springs and HD retainers not only to take advantage of the higher rpm capability but also replace the older weaker factory springs in the engine. I would freshen the head and do a multi angle valve job to give a little extra flow and maximize the reliability of the top end.
Are you going to do high compression pistons or forged connecting rods? This will determine what other parts will be added to support this type of engine.
The ignition should be upgraded with better spark plug wires with silicone shielding for a higher voltage. The use of a capacitive discharge box, such as an MSD SCI, and an upgraded ignition coil will be the parts required to maximize the combustion energy.
Depending if you go to a higher compression or not, the fuel system should have at least cleaned and balanced injectors with a very good fuel filter such as a factory 300ZX filter. I recommend getting an adjustable fuel pressure regulator and dial up the pressure an additional 5-10 percent resulting in an increase in the injector flow.
The springs can be sourced from many different companies but for handling the Whiteline, Eibach, H&R, or Suspension Techniques would be great for a street driven car. You may hear alot about the Ground Controls but unless you are going to corner weight the car and then do a race alignment they are overkill. They do have a fair amount of height adjustability but they cost twice as much and if they are set too low it is not only out of the working range of the strut but also will be detrimental to the handling of the vehicle as well.
The struts are pretty much limited to only a couple of alternatives; the Tokico HP and the KYB GR-2 now. Both equally good and could come down just to brand preference.
One of the biggest handling improvements though is replacing the rear sway bar. Whiteline and Suspension Techniques offer extremely good replacements. I also recommend replacing the front swaybar and the endlink bushings with urethane replacements. I know that Whiteline has a replacement front bar and the bushings can be purchased from Whiteline or Energy Suspension.
The control arm bushings can also be from Whiteline or Energy Suspension, although I prefer the Whiteline replacements because they add an additional half a degree of positive caster which will improve turn in and center correction. I mention the products from Whiteline a lot because I have their entire line for the Altima (or Bluebird since they are in Australia) they have the most complete product line up and I know it all fits well, quality construction, and is less expensive.
The brakes on the Altima are really quite good from the factory. Really the basics like upgraded street pads like the Hawk Ceramic, rotors such as Stillen/DBA or Brembo, stainless steel lines like the Techna Fit or Goodridge, as well as synthetic brake fluid like Motul or Valvoline are all I would do. The next step would be to get the SE rear disc brake conversion parts and after that KVR 13 inch front would be the ultimate front big brake upgrade for the Altima.
The mounts were available from Place Racing but I am not sure if they are still business.
Troy