fiberglass are 1970. The better of the two years that interchange 70-71. The 72 are totally different but they have replaceable studs like the fiberglass style in 70.
72 will not work on 70-71. But you can use 70-71 on a 72.
The 72 extensions have a shorter eyebrow lip. The 71 grille hits that lip.
Just some info for ya all to use so you get what you can use. Steve