Abody 4 speed pedals, complete

Does anyone know what the deal is with some pedal assemblies having the metal piece (maybe a guard) covering the large spring while others don't have it? Did only certain years of pedals have that metal piece and did it really serve a purpose? I have a set of pedals from a 68 Dart and they don't have it but I have seen others for sale that do have it.

On page 6-4, my 68 Plymouth Service Manual ID's the pedal set with the metal guard around the over center spring as Barracuda 383 Cu. inch (heavy duty clutch) I think this type of pedal set was also used on 340 cars.

Russ