A bare drive won’t work, if you’re connecting to the IIgs via the disk port then a 3.5” drive needs a case with a daisy-chain port. You can just replace the 800k mechanism in the case with the 1.4mb mechanism. However the IIgs will still only see it as a 800k drive. To use it as a 1.4mb drive you need the Apple II Superdrive card.
The only way you can connect a bare drive is via a Universal Disc Controller. Even then it’ll only see the drive as an 800k drive.
The only way you can connect a bare drive is via a Universal Disc Controller. Even then it’ll only see the drive as an 800k drive.