Stock rear TT wheels have a +35 offset and match well with the front of the car. So a +40 offset wheel that's 8.5" is going to sink in a bit more (possible caliper clearance issues too). Also going from a 245/45 to a 255/35 you loose about an inch of sidewall.
245*0.45=110.25mm 255*0.35=89.25mm
It may work but it's far from an ideal choice.
"The 300ZX Turbo is a dance; it's a song; it's rolling, roaring automotive art. There is no color that doesn't suit it. There is no mood-lifting chemical substance it can't replace." - Automobile Magazine