Got back to some more exploring in GT2 Test Drive, today I went through the American cars.
There wasn't as much to find, since a lot cars were already present in the garage.
The most interesting things I found came from Ford related cars.
These two things were the most interesting though.
When typing in the RS200 Rally Car code from the final, I got the Ford Escort RS 2000!
The Escort Rally Car is confirmed to be the Escort 1.8 GTI's racing mod, as that's what I got when entering the Escort Rally Car code into the demo.
Now it's time for some other findings:
The GT1 version of the Dodge Concept Car LM is confirmed to have been planned to return:
Strangely, the normal Concept Car is not modelled yet.
It appears that either the name of the Ford GT40 would've changed to "GT40 Le Mans" when you race modified it, or it was just an early version of the GT40 Race Car. It seems to be the former, as I got this car when typing in the final GT40 RM code.
The Ford Focus Rally Car was called the Focus WRC '99 Group A, and in the demo it uses a standard Focus as a placeholder.
Either the Shelby GT500 KR '68 didn't have the "KR" part originally, or the non-KR version was planned to appear instead.
The Plymouth Muscle Car is incorrectly referred to as the Superbird in the demo:
The Ford Puma 1.7i Zetec was referenced as the Puma 1.7i DOHC in earlier builds:
Now it's time for minor logo differences:
Some Chevrolet logos used more generic font:
The Ford Focus 1.8 Zetec logo didn't show the 1.8 part. Plus the Focus logo was black.
The Ford GT40 logo was completely different. The "GT" part was reused from the Mustang GT, with a generic "40" slapped on at the end. Probably used as a placeholder.
Finally the "Ghia" part in the logos of every Ford that was a Ghia was misspelled as "Ghla". I believe this still happens in the final Japanese version too.