Do you have the wheels on hand? On the back of the wheel either on the hub or the spokes the offset will be stamped there. It will be "ETXX" with the XX being the number that represents the offset.
The 4.5" center to center holes are the ones you'll be using (in metric that's 5x114.3 ). You might also want to look into getting hubcentric rings. These will adjust the hub bore of the wheels so that it will match the hub bore of the car.