Hi there,
I used to work for AC Delco at that time, and the correct replacement battery was a 75Z72. The Corvette was the only car in the catalogues at that time, calling for this battery. I no longer have any of those books, but it seems to me that it was replaced by a 75A72 battery. If I remember the 75Z72 had a slightly, and I mean only slightly, higher cca than the 75A72. It has been almost 20 years since I have seen that listing, but it seems to stick in my mind. Any AC Delco dealer should be able to give you the current replacement battery listing for that car. Hope I was able to shed some light.