Yours is the autofocus model by virture of the box attached to the left hand side of the enlarger. You also have the remote control unit which you will find handy when programming and printing. With the autofocus I would think that you will need the 50mm lens as this is what the calibration system uses for calculating the focusing distances although you may be able to trick the sytem into believing it is a 50mm lens since the focal length is not that much different. When it comes to calibrating the 105mm lens thay allow for a 100mm lens to be used instead. The limited information I have on the enlarger shows only the Cobineg carrier with the Binema masks being used but if the Bimaeg is marked for use by Durst it should do the trick.

The black metal piece on the right hand side of the enlarger head contains a grey disk for calibration of the densitometer. The black door behind it is for setting up your basic filter pack. There is suppose to be a special tool for this but a small screw driver will work. There is a process by which you will need to do to set up your lens to autofocus. It is not difficult - you will need the instructions for the Elite model though.

The bimaneg looks the same as the cobineg except for the red handles on the carrier.
http://cgi.ebay.fr/durst-Bimaneg_W0Q...ayphotohosting

The integral part for the densitmoeter actually sits below the neg carrier ( my mistake). The black plastic handle below the carrier pulls out and that is where you set the type of film you are projecting (B&W, transparencie or Colour Neg) for the process.
I have an old Durst price list somewhere and I will try and check to see if they list the parts for the AC800.

Gord