You can mix & match any of the wheels 28 thru 35, 21", 19", 18", 17" or 16" (except for the 28 AR wheels). But like 1930 Coupe said in post #3, they will fit but look funny.
I ran all sorts of Ford wheels on my '30 TownSedan in the 1970's, including 21" wheels. My thinking was that the larger 21" would give me greater speed and better gas mileage. I don't know if it ever did, but what I do know is that the larger 21" wheels hit the brake rods when turning tightly.
Depending on the tire selected, the outside diameter of the wheel/tire might not be any different between a 28/29 and 30/31 wheel.
21 inch tires range from 29.75 to 30.79 outside diameter and 19 inch range from 28.9 to 30.5. . Even going from the smallest 19 to the tallest 21 would net less than 1 inch in vehicle height, and the difference in speed would be within the margin of error in your speedometer. The difference in top speed would be in the area of 1.5 mph.