I have tried searching around and have read at least 50 threads on this but they dont really answer my question, based on that im guessing that there could be a problem but I figured I would ask.

Has anyone tried putting 350Z 18" track wheels on an 06 G35c?
Then would it be possible to use yokohama advan neova tires (235/40/18F) and (265/40/18R)?

I am guessing that going from the stock 19"s to the 350z 18 with that tire might give the VDC problems but this was just a way i thought to get lighter wheels and really grippy tires for a good bit less than 3k.

p.s. I know this should be in the tire and wheel section but I was hoping to get some answers here.

I don't think the track rims will be a problem.....I believe a couple of people have installed them on the G.

If the tires are within the same diameters as the coupe you will be fine.
I believe the rear diameter for the 18" coupe is 26.8
and the Front diameter for the 18" coupe is 25.9

I put 4 of the same size snow tires on my coupe, and had no problems with the VDC. They were 26.7, so use your own judgement.....but I don't think it will be a problem as long as you stay within the 3% range. Make sure the rims will be able to handle the width of the tires as well