What's actually hitting? Is the wheel cap hitting the threads on the spindle where the nut for the wheel bearing is? Or is the wheel cap hitting the hub on the disk brake rotor because the center bore for th wheels is too small?
If it's the first one, find a taller wheel cap. If it's the second one and you don't want to (or can't) have the center. Ore enlarged you might have to look at a set of wilwood brakes with a smaller diameter hub.
I would just measure the wheel cap and use the dimensions to find a taller set. I actually had to make the wheel caps on my duster because the center bores had to be machined to clear the rotor hubs, and then I had to make them deep enough to clear the dust cap on the spindle.