I just saw that the Floppy Emu creator just released a new version of the //c drive switcher and a new adapter for the standard disk II card to work with the model C FE dual 5.25" mode.
The new version of the //c switcher is functionally the same on the inside, so if you have an old one you don't need to swap it out. You can use the new external piece with the old internal tap. So no need to open up the //c to use the new one if you have the old one installed. The new internal part is a bit smaller and should fit in a Laser 128 better now.
For models with a regular disk II card installed, the adapter connects to the drive 1 header, and then runs a single wire to the drive 2 header. Then the FE connects to the adapter.