The stock gas pedal on my '00 Mustang was about 1" lower than the brake pedal, making it almost impossible to heel & toe on a downshift. I did the Mustangworld pedal raising fix but there still remained about 3/8" difference in height between the pedals. Grrrr.
Ford raised the gas pedal on the "Bullitt" Mustang, so I purchased a Bullitt pedal set. It raises the stock pedal about 1/2" - not enough. But if you then add the Mustangworld fix, it comes out just right. I now have accelerator and brake pedals at exactly the same height.
Ford stock numbers (Ford dealer parts department)
UPDATE: 8/12/02 -- After driving with these pedals for some time, I find that it is still very difficult to heel & toe. The accelerator and brake pedals are now the right height, but they are too far apart. If I was going to do this over again, I'd probably opt for one of the pedal cover kits that adds an extension on the left side of the accelerator pedal. The Pro3i kit pictured below is typical, and costs about $50.