Anybody running 17" Cobra Bullit rims on a Duster

Hi guys ! I am fully interest in change my wheels, I'm actually using 235/60 R 14 front and rear, I would like to try 235/40 R18 at the front and 275/40 R18 in chrome Mustang Bullit - Bullet Wheels 18x9 front and 18x10.5 set, but, I'm not very sure about my backspacing and I don't have my car now because I'm far from home and is not possible for me to take measures by my self. Could you please help me on this ???
http://www.oewheelsllc.com/Mustang-Wheels/1994-2004-5-Lug/17-Mustang-Bullitt-Bullet-p5939497.html
This is the link of the wheels I like but in 17" same bolt pattern, I think rears are going to look wider to outside (please correct me if I'm wrong) and it's great for me because the distance between rims is smaller rear than front and with this rims they are going to look the same size. (I hope you know what I mean) what I dont know is if they are going to fit (Backspacing) on my Dart Sport 74 ? and if I have to ask for a different spec. How I have to do it ?
Thanks for any help in advance ! I will wait for your answer !
PD: Sorry about any mistake, I,m new on this !