Well, the handy dandy offset calc says you'll have 4mm less clearance to the struts and 22mm less clearance to the fenders than the 17x8 cobras.
http://toy4two.home.mindspring.com/offset.html
Dont know if they will fit, but I think the strut clearance will be the biggest factor. Try to find some guys running 18x9 (or even just 18's) and see what offests they use. Plug the numbers in the calc and see how the saleens compare.
99% of the questions in the wheels forum are about offset and fitment. The gurus over there seem fed up with these kinda questions but they answer them occasionally. Look thru the first couple of pages and see if someone asking about a similar setup got a response.
Ive been looking at wheel fitment for a few weeks now. Glad I could help...
BTW, I like the saleen wheels, but 18's are a little too big for my taste (and budget). The black ones are lovely though.Here's link to a seller of replicas. Dont know how their prices compare, but it should give you an idea.
http://www.wheelreplicas.com/