I have converted both Altronic & DC headsets. The DC 10-80 make a particularly nice conversion. You must use gel seals and the DC extra comfort ones are dramatically better. On DC 10-40 headsets you need to buy additional volume potentiometers from someone like Farnell. Its worth paying extra to get the single cord option. Add the DC padded headband and its quite a nice thing.
The DC conversion is significantly better than the Altronic conversion. I think it is because the DC ear cup is thicker plastic which helps block out some of the frequency spectrum where the electronics are weak.
I bought some secondhand DC headsets from ebay to convert, but these days, if you don't already have the headsets, you might be better to buy a set of lightspeed ANR headsets.
The ANR conversion guys in the US (forget the company name) are easy to deal with and the package is delivered quickly. Its quite a bit cheaper than buying them here.