That clearance can change depending on your ride height and hitting bumps or low spots when turning, like driveways & such.
5/16" doesn't sound bad depending an how you're checking it.
Closest point should be bottom corner of fender in front of the tire.
That's actually easy to trim back at a 45-degree angle with tin snips and will barely bother the paint if you're careful.
I've done that on a couple of Dusters and early B-bodies.
Car is sitting on the garage floor and I bounced the front end up and down my hand to make sure front end is settled after putting the tires on. I than turned the wheel left and right and checked clearances. The closest point is the bottom corners of the fenders, everywhere else there is plenty of room. Just didn't know if 5/16" is enough under normal driving conditions.
