don't think nismo's engine will be such hardcore, they are all about 'balance' but not high power.
even a 400R will find very hard to acheive 385rwkw if he don't mod it.
400R is only using nismo N1 engine with full fogre internal (piston, rod, crank shaft) and 2 x N1 turbo, which u can buy from nismo today as well, the only think special is carbon fibre drive shaft and it was totally built by nismo with limited number.