The best thing to do would be download the LP560-4 I helped with:
http://www.racedepartment.com/true2...lamborghini-gallardo-lp560-4-superlegera.html
Look at the setup of the files and folder structures and mimic this.
You need to extract the GTR2 .GTR files and then convert them to Race07 format and then sort them as per how the 560 is.
Then go through each file (.inccar, .eng, .sp, etc) and edit them individually to suit your new 670-4.
This should get the car at least to the car selection spinner (plus or minus a few errors)...
Then you need to start bug fixing to get the car on track.
Then to bug fix the little things one by one.
It took me 3 months of trying, to get my first 2 cars (2008 V8 Supercars) completely in game and "finished" ... maybe 500 hours ... But, this was some of the first cars added to Race 07 and much was needed to be discover exactly how to do each step...
You can now find many mods to use as a reference...