If it is original, it could NOT have hubcaps! See pix…all ’66 Coronet 500s had full wheel covers on 14" steel wheels.
While 8" wide wheels would clear easily in the front, out back, anything over 7" gets very tight. No matter which width you wind up with, the offset should be near zero.
Most guys throw in the towel and opt for larger diameter wheels due to the poor selection of 14" tires. If you want to keep it a pure resto, with repro tires, though, that’s cool. You might also find some 15" Dodge C-body wheel covers that at least look “period correct”.
Remember, too, that spirited driving and wheel covers don’t mix. Zero brake cooling, and loss of covers due to wheel flex. Just sayin’….
Paint code 999 = special order. Basically, anything the buyer wanted!