65 Barracuda Disc Brake Conversion Help Needed

From a turning perspective I think the shorter tire would be plenty, you don't actually need that much clearance on turning. But, I don't think wider would help at all unless you changed rims. Losing the drop spindles won't pull the tires in closer to the frame, other than the "axle" location/height they're the same as the 73+ spindles. Raising the ride height would help some, but you'd still be hanging the wheels all the way out to the fenders.