I have the M601 with a Sevoneg adjustable glass neg carrier (35mm to 6x6 and all between). According to the info on Ollinger's site, the 600 is the older model and has a focusing device similar to the M301 (the red-green doohickey). For a lens plate I have a Lapla for 6x6 and a recessed lens mount for the 50mm lens, a Setopla 2839. I also believe the 600 has a different condenser setup (3, I think) where the 601 only requires two condenser lenses for 35/6x6. The third condenser lens on the 600 is for 35mm use. I'm guessing but I believe the 600 resembles the m300/301 with the focusing aid and lens panel arrangement.
If I recall, my M301 came with a 25mm lens panel but I could be mistaken. What lens is coming with the enlarger? The older componons were 25mm thread.