I don’t know what enlarger you actually have. The D2 and the DII that preceded it are manually focused. The D3 Automega and D4 Auto-Chromega enlargers use a cam specific to each particular lens to operate the focusing mechanism. It might be that you have a D2 head on a D3 or D4 chassis. The head designation does not lable the chassis model. That is usually found on the back of the column.
You can get more information about these on the KHB Photographix site. It lists which dichroic-filtered heads fit. Don’t waste your efforts and money on the older Chromega heads using dyed acetate filters. They’re no longer made and will have faded uselessly by now. A older Chromega head is shown mounted on the D4 on the following page. On the KHB site clicking on the photo of the enlarger model chosen will take you to the page for that model.
http://www.khbphotografix.com/omega/Enlargers.htm
There are comments on the KHB page for the Chomega heads that speaks of the impracticality of converting an acetate-filtered head to dichroic filters. You can read it in the folling link:
http://www.khbphotografix.com/omega/Chromega/Chromega.htm