I've been on the forum for a long time, but rarely post. I collect and restore Bulovas; I've got dozens of models around and about. After my third '58 His Excellency acquisition I noticed what may be a clear identifier between the 10k RGP and 14k gold models.
Here are model's 'E' and 'D', respectively, with their 10k RGP cases:
Now, here is the 'F' model (although in the ads there is a reference and at least one photo of it being "two-toned", which is not altogether accurate on some I've seen, mine included):
As you can see, no "10k RGP" or "10k Rolled Gold Plated" is mentioned anywhere on the back of this case. Interestingly, nothing at all is inscribed on the inside of the case, either. But, due to process of elimation and the obvious comparison in 1958 models, I'm thinking that this **MAY** be a fairly reliable indicator of a 14k gold case unless someone can come up with further variations to, again, muddy the waters.