hey mate, im happy to share any info you might want, also my build thread is prety detailed. i see your familiar with it.
i have been asked the question about rego and by my understanding you can legally engineer and register up too 6litre na.
why you would need to then turbo the car is beyond me.
the conversion is very straight forward and almost the easiest i have done.
the fact you can buy a ls2 crate engine complete from intake too sump for 4k also makes it the cheapest.
the mass of aftermarket parts whether it be cams, rocker gear, valve springs, etc is readily available and cheaper than any nissan part.
I love turbod 6s, but they dont compare to the savage torque of a healthy v8.
good luck.