Considering it is white, I'm wondering if it was on a truck. I have a 79 Ramcharger H wheel, but I think it is a 5-4.5 5.5" wide, not 6. My 81 Power Ram 150 had 5-5 6" wide wheels.
I loved my Ford F-series trucks but was NEVER a Ford car guy. The only Ford car I had owned was a 1978 Mercury Cougar which I took "on a trade" from the guy who bought my 1981 Dodge Diplomat. I fixed the mechanicals and quickly sold it. In 1995 I bought a 1990 Mercury Grand Marquis Colony Park...
I agree with Big_John, "There's enough guys that can decode it and maybe tell you what it originally had". EVERYONE here will help. There is a wealth of knowledge and all of us "C-Body guys" like to share as well as absorb information.