I have an '80 Malibu that's a factory 4 speed car. From what I know, most of the factory 4 speed cars came with a shifter that was made by a company called ITM. That's the shifter that's in my Malibu now. I went looking for a Hurst shifter for the car. They are hard to find now, but they still show as being available from Hurst online. You need to get 2 items from them, the Hurst Competition Plus shifter, and an installation kit, neither of which is cheap, but it was about all I could find. I was searching local online ads here several months ago, and I found a gentleman who was advertising a factory 4 speed Hurst shifter assembly that came from a '78 Cutlass. The shifter was complete, and in good shape, with an April 1978 date code stamped on the shifter assembly, and it was considerably cheaper than getting the parts from Hurst online, so I bought it.
As for which GM A body cars from 1978 and I think 1979 had the Hurst shifter as a factory option, and whether it was listed as a separate item on the factory option list, I'm not sure. I have one from a '78 Cutlass, GP403 has one from a '79 Grand Am, and you have one from a '78 Buick Century, so I'd have to assume from that info that you could get it from Oldsmobile, Pontiac and Buick. I don't know about Chevrolet. Maybe someone else can chime in with some more info.
As for which GM A body cars from 1978 and I think 1979 had the Hurst shifter as a factory option, and whether it was listed as a separate item on the factory option list, I'm not sure. I have one from a '78 Cutlass, GP403 has one from a '79 Grand Am, and you have one from a '78 Buick Century, so I'd have to assume from that info that you could get it from Oldsmobile, Pontiac and Buick. I don't know about Chevrolet. Maybe someone else can chime in with some more info.