I was advise that besides tuning both carbs (still getting spark plugs 4 and 5 black), if i replaced the following parts, the idle could get smoother below 3,000 RPM: 

 

K & N E-2910 Air Filter

 

http://www.knfilters.com/search/product.aspx?prod=E-2910

 

 

Magnecor Spark plug wire set:

 

http://whiteheadperformance.com/products/magnecor-competition-kv85-8-5mm-spark-plug-wires-6524-datsun-240z-260z-280z-280zx-l24-l26-l28/

 

 

My car has a petronix ignitor and 3.0 ohms petronix coil.

 

 

If upgrading these parts will give me a smoother idle and less hesitation, i will make my order. Otherwise, if it is useless, i wont bother! Please advise!

 

 

You can continue to throw good money at a poorly tuned engine, but I'd suggest:

 

1) Start with ensuring the valves are adjusted corrrectly

2) Confirm emissions gear is working as designed, or blocked off & no vacuum leaks (and also check your PCV valve to make sure it rattles freely)

3) Set timing to specs

4) Tune the carbs

 

Also remember, a 40+ year old car is not going to idle like a new modern fuel injected car, it has its own character with the gurgly idle.  You may also be due for a full engine rebuild (top & bottom) if its never been done.  Between old worn rings, bad gaskets/seals, and years of gunk growing in the engine, that could add to a poor idle.  Check out what was living in my PCV filter of my '72 240z and the carbon buildup on the cylinders:

See what vacuum you have, 15 hg and above is good. You'll need good vacuum to actuate the a/c idle increase.