Moving along......
This is a comparison of the GM WA5111 (521) .... called "Truck White" vs GM WA3967 Antique White (11) aka Dover White (50)
The WA5111 is definitely brighter and has more of a blue tint to it, the WA3967 is definitely more yellow and "creamier" looking by comparison.
Both were available in the years between 1969 - 1972 so either one could have been valid for a wheel in that time period. I guess if nobody knows for sure I'll paint two wheels with WA5111 and two wheels with WA3967 and mount tires and put them on opposite sides of the truck to see how they look against the rest of the paint, etc.
-G