Rochford Tyres (
www.alloywheels.com) have a nice selection of wheels available for the Cougar. They supply the spigot ring and the new nut set included in the price. Some styles are pretty cheap. I got mine from there. It was cheaper than buying locally even if you include the shipping to the other side of the world.
ET35 offset (for 17x7) looks the best in my opinion. I wouldn't want the wheels sitting any further under the gaurds now I can see how they look once fitted.
I put 225/45ZR17's on my wheels. Speedo is 0.5km/h out (when it reads 100 I'm really doing 100.5). I had it checked on Friday. With the standard size 16" wheels/tyres the speedo was out the other way (showing 100 but only really doing 97).