75 is the only different because 75 is the first year they used a catalytic convertor so the floor plan has an indention under the driver side front seat where the catalytic convertor would reside.
Odds are your catalytic convertor is long gone, long ago. You can Just weld a 70 to 74 floor pan in the car and not worry about it.
In the rare chance your car still has the catalytic convertor, that's a good item for the scrap pile.
The old convertors do not have the value as the new ones because they were primitive and probably worn to nothing after 45 years.
Good luck and great to see another 75 live on.
