Its always difficult to figure out how to present and share information since there are so many different ways to arrange the information, so many variables and we each learn/process things differently.
Nice clean unrestored are difficult to find - and their numbers are shrinking daily. At the same time any restored car is going to have old information, things that were incorrect when restored and it can be disrespectful to comment on those details unless we've been asked by the owner.
Don't think you will find an exact match but that should not be a deterrent since the same people that painted a T code or even a Cougar at Dearborn in December used similar products and processes as they did on your car. 390 cars in general are difficult IMHO to find pictures of since few were left original though have helped build a number of 68 S codes that were successfully shown nationally.
There is no easy button. Most seem to focus on an area, ask questions, evaluate responses and findings than move onto the next subject. Too many variables to cover each plant, time period, all the options, accessories, body styles and so on.
Looking at what has been posted I see a late 68 Dearborn T code coupe thread at this moment. Speaking of my collection of pictures I have few good undercarriage pictures for 68 Dearborn cars as I do San Jose - just due to access and it seems few owners focus on anything other than engine compartment, interior and exterior.
I invite you to post in the 67-8 section and start a discussion. Hopefully examples will be offered. In the meantime I'll see if I can post a thread or two of 68 Dearborn examples.
Are there any photo threads, online links, etc. to survivor cars for 1968 Dearborn built Mustangs? I'm just starting into the restoration of my 12/19/67 Dearborn built, S-Code 68 GT Fastback and I'm starting the research on the undercarriage finishes so when I shoot the primer and such I know the pattern, etc.
I have a good grasp of what gets what color sprayed where, but would love to see untouched examples and especially cars concourse restored as a reference.
Hopefully you had some original floor color (firewall rearward) as well as front frame color from the original panels.