7.5" rears were introduced in 1975. I believe a Monza, Skyhawk & Starfire had them. The 6.5 was continued in the Vega except for Cosworth Vega which I believe had the 7.5" . The S10 axles only fit the 7.5" rears, so you need to make sure that is what you have. My 75 Monza has the 7.5" rear.......
The original question was in regards to a V8 Monza, so it has the 7.5" rear.