I was confused about this too. The Ford distributors like the duraspark II are .467 as is the small hole in the block where the
oil pump shaft engages the distributor. The different sizes for the distributor gear is up higher on the shaft. for after market like MSD and Pertronic's the shaft "steps" up to .500.
As for the distributor gear material for the billet steel cams, I am running a COMP cams retro roller rocker cam. I used the Crane distributor gear 52970-1 from Summit Racing on my Pertronix PNX-D7133700 also from Summit.
The Pertronix III uses the black distributor cap like on the period correct Chevrolets. It looks almost identical to the Ford distributor caps except it has (in my opinion) the better mounting screws instead of those clips.