Rule of thumb for width of tire on a rim is add 1" to the rim width.
A 10" wide rim will be 11" wide. The width of the rim is to the bead not to the rim edge. Most tires I add 1" to that so you have a total width of 12". Subtract your backspace which might be 4" and the outer edge of your tire would be 8" from the mounting surface.
Put a straightedge on the hub and use a tape measure to measure from it to any interference points on your fenders. Just remember most inner wheelwells curve inward right away so depending on tire height you need to measure up inside to. Also remember you need clearance for tire movement. Add another 1" on both sides.
Here's a link to cragar. Click on specs and a pdf will come up with all the info you need.
http://www.cragarwheel.com/products1...61SSSuperSport