1971 Duster Twister Rallye Wheels without Center Emblem?

How did the '71 Twister model (available only with slant 6 or 318) manage to employ the rallye wheels without the center caps? Was the wheel bearing grease dust cap plain or chrome? Anyone have an actual close-up photo? I have some rallye wheels and I want to duplicate whatever the Twister model came with from the factory. Thank you.