Anyone know if g37S wheels will fit a 2003 G35. If so which lug nuts do I need G37S lugs or G35lugs?

 

You'll be OK but the offset on the 37 wheels is a bit more conservative if you're going w/ coupe wheels, the sedan offsets would be about the same. so they'll sink into the fender a bit more if you're talking about 03 coupe wheels compared w/ 37 coupe wheels.

The lugnuts need to be the mag-style w/ washers like this

 

They will fit. just get them.