Hi Erik,
The R is Torch Red.
Is the interior ALL Red? If it is that would be unusual but would fit the code.
Another possibility is that it was a real early 55 and they hadn't started using the X. The CTCI link below states that early ones only used the B. Check the Date Code on the 2nd Line of the plate. That is probably the most likely.
Here is the link I used.
http://ctci.org/decoder.php
If you have not joined CTCI it is worth doing. They have lots of Manuals and info for restoration.
Also, if you have not registered it at
Thunderbird Registry - Home of Horizons Unlimited
do so and John Rotella there may be able to tell you something about it's history if it has been registered before.
Do you have the European speedometer or was it a US import with MPH?
Jim