jccjr1982 is dead wrong. god, i cringe when people dont know what they are talking about. infiniti G35s are NOT THE SAME CAR. the easiest difference? the name. duh. if it has an entirely different name, its different...end of story. the G35 has a nice 3.5L VQ engine with double cams and fuel injection, good for about 280 ish HP...slightly similiar to the skyline. however, the aerodynamics, suspension, chassis, transmission, and body style are all extremely different.
the skyline is a COUPE. its a very long coupe, but it is a coupe. only this year have infiniti g35 coupes come out, and they are quite expensive. the skyline is more of a racing car, it comes with brembo brakes (stock) and a stiffer suspension. it also comes with 300+ hp (R34), despite the gentlemans agreement. (fact: people have bought nissan skylines and dynoed them after driving them home, doing no tuning, and they produced well over 280 HP. the most was about 330, give or take 5, by the R34 VSPECII. Ttoyota did the same thing with later versions of the Supra, but not exactly as much as Nissan). the skyline GTR has a twin turbo engine system and is all wheel drive. ATTESA-ETS and SUPER-HICAS are on the skyline, whilst only the ATTESA-ETS is on the infiniti G35x (which is 4WD).
ok, ill stop ranting. to answer your question: you can LEGALLY import any R33 skylines that were made in between the years of 1996 and 1998. if you wish, you can look it up on the US importation list, i dont have the link on hand. GTS, GTS-T (or whatever they had) and GTRs are all legal from that time frame. however, they still have to pass emissions, which requires a great deal of work. if you buy the cheapest skyline, the 96 GTS (or GTS-T i think), itll cost you about 10k at the least, excluding shipping to some east coast port. then emissions and legalization...but itll be under 20k, maybe under 15k if your very picky.
Motorex was the company in california. in a nutshell, they arent up and running anymore, so dont even worry about them, they cant help you in any way..the owner is in jail. so yeah.
oh, by the way...any and all upgrades to the nissan skyline GTR, no matter how mundane, will result in a relatively large boost in horsepower. exhaust systems, *any* turbo upgrade (stock turbos are ceramic), throttle body, computer chips...for some reason, they provide like 150% horsepower to the skyline compared to any other regular car. and the RB26 engine is remarkably resilient.
good luck getting it into NY...i live in CNY, ill get one eventually haha ;) i hear theres only two or three legalized in NYS, all in NYC i believe.
edit: its not a ceramic engine. its a cast iron block engine with an aluminum head. and to add to that, you dont need to have it changed to left hand drive, you can keep it in right hand drive, it is perfectly legal. why? post office trucks can drive on the road, and they are RHD. (plus theres no law that says they cant =P)