Restrictor Plate Removal: This will allow you to go faster at the tracks with them on.  To remove the restrictor plates at Daytona, Daytona Night, and Talladega change the line chassis_type = 1 to a 2.  You can also put restrictor plates on at any other track by changing the number to a 1.  You can try any chassis type at any track by putting in one of the numbers below.

1 = superspeedway with a restrictor plate
2 = speedway
3 = short track
4 = road course
5 = superspeedway without a restrictor plate

Roof Flaps Removal: This will allow you to get airborne easier.  This edit is not in the track.ini files like all the other edits here. For this one you have to edit the player.ini file.  This is normally located at C:\Papyrus\NASCAR Racing 2003\players or wherever you installed the game.  From here you chose the folder for the player you want to change and the player.ini should be in there to edit just like the track.ini files.  Change the line employRoofFlaps=1 to a 0.