I Couldn't tell you 100% For Question 1, But wat i have been told is that the r33 is a stronger gearbox the Casing is thicker and the Standard syncroms are much stronger also....
I could Tell You About the Second Question ... I have had the luck of installing a Nos System to a gtr r33 with a mate of mine... The Fuel system was already upgraded such as Injectors, Pumps, Surgetank etc,...
But Using Nos does not affect the injector capacity i can tell u that
Installing the Nos system was just a simple procedure...But Placing the Jets into the plenum or casting is time consuming
Hope i could have helped