some information
I just obtained a D6, and it has the wrong movable condensor in it. The D6 has a knob that moves the lens, but mine came with a lens from an earlier model. The earlier model has a number of shelves that you slide the lens into. The problem is that there are two shafts in the back of the lens compartment that interfere with inserting the lens, so a previous owner hacksawed the corners off the lens mounting frame so it would fit. I don't know which model you have, but you may have to modify the lens holder depending on which lens you get. If you have questions about aligning the enlarger, I just finished doing mine. Good luck.
Best regards,
Chris