you are best to balence the car from the first build. I didn't put a pedalbox in mine cause i'm miserable, but i put the nav seat practicably in the back, which gave me a 56/44 weight distribution with driver and nav in (58/42 static). Most other gtst's are 60/40.
The GT-R have better weight distrobution cause of the heavier rear end, box/transfer case etc. But your still best to move as much as you can as far back as you can. If you don't do it now, you never will