Can anyone tell me what these seats are out of? Fairly cheap but im not sure about the application.

 

Heres a pic of the brackets on bottom

 

Are these gm?

 

Those are Cutlass Salon seats. That style was used from '73 to'76 & they were unique to the Salons. Most were cloth but I believe vinyl was standard. In '77 Salons went to the std. gm high-back buckets that all the A-bodies used.