I believe there are 2 different styles of the larger shields.
There is the smaller one that goes thru the frame rail. About 8" long and looks like a water trough. and then there is the larger one on 1970 ECS cars. Then there is another larger one on 1971 cars, shaped slightly different but it attaches and it's purpose is the same as the 70 version.
This is the 1970 only version of the main shield. I don't think I have the smaller trough looking one.

I know someone was repoping both versions of the larger one at one time, but I've not seen anything in a couple years on them.