Those are side mounts. Judging from Roas' pics, you need these as well as the subframes so you can mount the bucket seat onto the subframe. If you get recliners you only need the subframes.
You can always get universal subframes but they may require some drilling/modifications.
That is correct. You will need the mounts for the seats (universal) and a car specific subframe. The subframe can then be mounted on the original sliders.