Nhbenz, I've been trying to find the correct ID of those shield-emblems for over 20 years. If you've got solid proof that they are a radiator-cap emblem, I will praise you to everybody in the civil war relic collecting community for absolutely eliminating these things as a "Confederate saddle-shield."
Important note:
As the photo below shows, the shield's body is curved, apparently to fit smoothly against a hollow metal tube or similarly curved metal surface. If for a tube, the tube's diameter would be approximately between 3 and 4 inches.
Notice that the three mounting-holes in them are strengthened by a raised flat rim encircling the hole. That indicates these shields were made to be attached by screws or rivets. They clearly was not intended to be attached to leather or cloth.
I've personally seen them with the letters A, C, E, F, M, N, T, and U. Do you know what the letters represent?