That is a negative on the 1979 start date on the white bottom black top batteries for 3rd generation Mustangs. 79's had a white case with a red top. Don't know whether it was the same vendor or not as I have never been able to get any credible information on that. I owned an 83 GT that had the original battery in it, but I don't remember what color the top was. I think it had a red top, but I wouldn't put a great deal of faith in that. I also thought my ex-wife was the greatest until that went belly up. 82 used a battery like the 79's. From the info I've been able to dig up, 84 was the first year for the white case black top Motorcraft batteries. I also owned a 92 F150 that had a white case black top Motorcraft original battery in it, but it was a BXT-65C and not the BXT-58C that a Mustang would use.