This is what the D70 autofocus module looks like mounted in the camera. It is mounted at the bottom of the camera chamber below the main imaging sensor.

While the imaging sensor faces the front of the camera body, the AF module faces the top of the camera body and is fed light from the lens through a beam splitter in the main mirror on to a submirror. The submirror then redirects the light down to the AF module.

There are five slots. (One is partially obscured near the bottom of the photo.) Notice the central slot appears to be the cross sensor. I presume each slot corresponds to each of the D70's five AF brackets. Each slot then must be able to view the two split images that arrive from either side of the lens.