I think the custom = deluxe were all metal, if I`m not mistaken that would mean someone changed out your rear ones for the std. which were plastic...

I had in my 69 w de luxe interior metal up front and plastic in rear (somebody re-worked my car once..), but I went the inexpensive route and bought two plastic ones for the front...

but I am not 100% sure on the 67 originality stuff...but I think the metal ones in 67 had the Fisher coach body on them vs the GM mark on 68-69