I can't say that I've ever heard of a 3.5" backspace on a first generation Firebird or Camaro. You would have to run some mighty skinny tires or else they would stick out of the wheelwells and look silly! I know for a fact that the first gen Camaros used a stock 4.5" backspaced wheel, and the Firebird and Camaro are the same body. As a matter of fact, all A and F bodied GM cars used a 4.5" backspacing. A 3.5" backspaced wheel would seem like it would be for todays cars.