the sedan has a tighter engine bay. nothing is impossible w/ welding and crap. my teammate just installed a LSX v8 swap into his 350z. i have the first turbonetics 6mt sedan 2006 in the country.... i had to modify parts to make it work from a coupe b/c of the tighter engine bay.I have heard of RB swaps in the G coupe, so I don't know why you couldn't do the same to the sedan.
yes I saw a few picture of a G35 with Skyline Rb20 Det in it.
Might ,look at this