Jerry may have known what he's trying to say, but the wording isn't quite what it should be. If you work from the axle housing flange width rather than the axle flanges themselves where the wheel actually mounts you'll be something around 5" too narrow. Unless you've got a lot of experience with a certain configuration, what Em said above is the most accurate. You need to figure outside clearance to the fender, inside clearance to the inner fender panels and any suspension components that might occupy real estate that could interfere. Even working off someone elses similar car could be a gamble if you're pushing close to the edge on either side. Add to that that cars from that time weren't built to as tight of tolerances as today so they may not even be the same side to side, so check both sides. Don't forget too, once you've got a static mock up to work to, you can't just figure clearances at standing ride height, make sure you figure in what happens when the suspension moves up and down as many inner wheel houses roll outward the higher up the panel you go, as do most fenders of that era.