Up until several years ago most people really only checked the LR weight in pan car racing. With the advancement of the cars and technology most everyone has gone to 4 scales in recent years. 2 scale use to be a little cheaper and simpler option (and for more limited ability levels/budget levels it still is) but nowadays you'll notice most all of the serious racers have 4. We actually dont even make/sell our 2 scale boards anymore since there was not the demand and they are a little more work to make on our end anyway.
You can turn the car around and get the front weight with a 2 scale, but the #'s generally dont correspond well to the 4 scale becase the height of the block vs the scale height is critical. Even different 4 scale boards can read slightly different so its important to be consistent and use the same board for a baseline if at all possible.