Technically you could, but it's going to have a little stretch on it.
Better to go with 265/35/18...but then you have to worry about clearance since you have Superdowns.

Also the rear offset is a little low...you want to be closer to +40...might have rubbing issues with the Superdowns and +30.

 

I have almost the same setup with my car. 18x8.5 +35 front and 18x9.5 +38 rears. I used the stock tires on both the front and back, and you will have a stretch with both wheels. It's not really that bad at all. I'm on F Sport spring though, but I have no rubbing issues at all. I used the website willtheyfit.com to see how the tires and the offset looked compared to stock. It won't help with how the fenders will sit but you'll see how the tires will look and it'll tell you how close you wil be to your suspension.

 

By the calculations you won't have any rub at all in the rear with the 255, but I agree with Sasnuke, you should consider the 265 tire.

Keep in mind that you're so close to what will and won't fit without rubbing, that even the particular make/model/type of tire you choose will make a difference.

In general, all season tires fit easier than Summer tires because they have a more rounded shoulder for a quieter ride. So there are 265 all season tires that will fit easier than 255 Summer tires.

If it were me, and it was this close, I'd still choose the 265. If you rub it'll be minimal.

 

I don't mind a bit of stretch on the tires, I actually kind of like it but ya I think ill go with the rims with stock tires and would probably need spacers to clear 350 brakes since the front would have +35 offset