Lee
The caps are metal and based upon the picture they are the early Appliance because of the very rounded curvature lip of the caps. Later Appliance had a sharper lip.
I had a set of these a few years back but sold them..I will try to find the pics.
Here are the earlier ones you can tell they match the caps in the side profile shot of your car.
http://www.classiczcars.com/forums/attac...mp;d=1310423299