First, do you have a menu option for "LE MANS CLASSICS"? If not, the issue is with the gdb files; if you have the menu but no cars in it then the issue is with the gdb not finding the cars.
My previous suggestion is to see if the cars are in their proper location and will appear in a different class. For that -
You need to edit the "class= " line in the individual .car files, adding one of the default P&G classes to it. Then select that class in the game and see if the new car appears.
For example, here is the class line from a Ferrari 330:
Classes="SIM_LM_CLASSICS, SIM_FULL, SIM_GTC, SIM_FERP3, SIM_TFL67_CLASSICS"
Here is the class line from a P&G Corvette:
classes="GTO2, CVRL_CRVT_Z06, PG1962"
Add one of those P&G classes, for instance GTO2, to the class line of one of the Lemans cars, so that Ferrari class line would now be:
Classes="SIM_LM_CLASSICS, SIM_FULL, SIM_GTC, SIM_FERP3, SIM_TFL67_CLASSICS, GTO2"
That Ferrari should now appear with the GTO2 cars.
The physical location of the cars' files is mostly irrelevant, as long as they are in the proper vehicle folder structure; the class designations control where they will appear (to the point of even having a specific car only appear at a certain track).
