I am with Randy on this one, I like them close to the body which is how the majority of cars were back in the day. Most of the older wheels are around 3.75" backspace (Halibrand, Torque Thrust etc). I usually set the wheel and tire package up against the car and work out the rear end width from there. My cars are narrower at the lower rails than at the top so I usually put the upper sidewall of the tire about 1/2" out from the body. If the car does get sideways and distort the tire it will move more at the bottom and there is more room there with the narrow lower rails. If the tire does get into the body you end up with those donut shaped scuff marks that were common in the 60's if you saw the car with the rear wheels off.
Roo