Appropriate Wheel Offset for 18" Wheels?

So I have actually have something worthwhile to add... I saw these over at GRM and for the price they may seem like a great deal! Not ideal for me but it gets me in the 18" crowd.
http://www.americanmuscle.com/charcoal-amr-18x9-0512.html
The only problem is that they are 30 mm offset I am looking for about 40 (I have a similar setup to 72NewBlue) FMJ spindle, eventually dr diff 13 disks, early RMS tubular control arms, strut rods, firm feel tie rods.

I also have a Diplomat rear 8.25 (this is a fantastic rear for my goals) with Grand Cherokee disks. Do you think these wheels will be "close enough" with some spacers. I plan an a 275/40 square set-up?