I had a chance to experiment further using the Nikon D300 with my old Nikon PB-6 bellows. Due to the grip on the camera, you first need to rotate the mount on the bellows 90 degrees. After the camera body is mounted, you can rotate it back. I put my old 55 mm Nikon macro lens (Nikon calls them micro lenses). This is what the setup looks like.
I used the LiveView feature on the D300 to focus. LiveView is the ability to use the 3 in. LCD screen and lets you zoom way in on the image. This is probably more accurate than using the viewfinder. I set the camera to Aperture Priority and stopped the lens down to F8. I let the D300 handle the exposure and color balance. I pointed the entire rig outside for lighting. Here is an example of a picture I took of a 20 year old slide.