Could you explain your question a little better? By "old rule", do you mean the old car?
All I know is that Dale SR's death sparked development for a safer car. The seat is positioned more in the middle of the car for safety, there's foam in between the roll cage and the body, the car is bigger (height and width). Smaller gas tank I think(and stronger If I'm correct). The obvious differences are certainly the new spoilers, the bumpers are alligned(and the grille is on the bottom of the front now) and the windshield is more vertical.
I honestly believe it will be a stock car. I mean, it will probably be the easiest car that they have ever put into LFS. All they gotta do is use bob's NASCAR mod and add a new body/fix the tires.