Adapter plate will cause the wheels to stick out around 1". This is not a great idea, and I'd be willing to bet you'll have tire to fender clearance issues. Just get 2 4.5" b/c wheels.
Whats the average cost per wheel? I know I got a good deal on these ones I got because they are near perfect and the guy really wanted them gone now! I still have quite a bit of room in the fenders of my 74 dodge dart sport.