This is a picture contrasting the shapes of two CD 103's (GAYNER and B) vs two CD 104 shapes (NATIONAL and {Pennycuick style}. The specific insulators were kind of picked at random and not to pick the most extreme cases nor pick ones that were very similar. Disclaimer: All four were not photographed together so there could be some slight variations in shape due to that but I do not think that invalidates the comparison.

I do not have specific height dimensions for the insulators shown here, perhaps a CD collector or others have physical examples that can be measured. Given my lack of any quantitative information about these pieces, I will quote the sizes in the Price Guide that the CD 103 is 2 1/2" x 3 3/8" and the CD 104 is 2 1/2" x 3 5/8"