Lord knows I've written down a few debatable tid-bits over the years, we gotta try to keep each other in line and corrected. Primary example that is not a direct hijack of this thread is that for ~20 years the "official" word was that the 65-67 C-code was not eleigible for the GT/GTA packages, but since about the year 2000 I keep hearing they were. Not very common since the upgrade from a C to an A was less than $100, but a C-code GT is not necessarily incorrect.
I want to back off from one statement, the GT package was not ENTIRELY cosmetic, for axample you had to have a V8 and you had to have a 4-speed manual or the C4/C6. It may well be that the latter is similar to the C/A discussion, nobody ordered the GT package and put a 3-speed manual in them but I've never seen a "real" GT with the 3-speed manual in it.
Since the GT package was a separate option package I'd say there were 428s in SOME 68 GTs. Although when the CJs came out mid model year and swept the Winternationals they were selling the CobraJet package fairly easily.
I love those FE's, a buddy of mine has one and just yesterday was complaining about the lack of an active aftermarket industry for them...sigh...all good things eventually end I guess.