Also your all wrong in regards to engine size:
It goes off how heavy the vehicle is, for example at my weight I can go 5.4l FI An 7l natro (I didn't know these laws at the time)
It's a calculation u do I just can't remember it. It's like times the weight in kilos by this number and that is the cc u can have. The varying factor being the number you times it by for FI/Natro
The chassis construction also comes into play, weather it be a one piece like a skyline or you can lift the body off like a hq