you'd end up with having to buy a sawzall to cut your rails to make the front shafts run to the wheels. then you'd have to modify the rear cradle to fit the rear mounted GTR gearbox, and possibly also figure out how your diff mates up to that. Then somehow mate the individual sensors to the R35 ECU (lets assume you're not gonna run a MOTEC or something on it just yet) to make sure you've got some sort of signal and don't limp around in diagnostics mode all day.
I'm sure there's a lot more, and lots of people will probably laugh at you for even thinking of such a wild idea... but hey I like to rub one out occasionally while thinking about putting it in Natalie Portman's pooper, so I too appreciate the value of wild fantasies. Stay strong brother.