The DS is exactly the same machine as a "standard" 743. The only difference is the standard it complies with for the department of forestery. From what i remember from my manual it must have a spark arrestor muffler to prevent bush fires and it has to have multiple filter screens (not sure why) over almost all air entry points into the engine bay. There were a few other things but all of which doesn't give the machine any advantage over a standard 743.
Being around 17 years old, i doubt all the filter screens are even there any more. I wouldn't buy the machine for any more than i'd pry for a standard 743 even if the owner says to you that its a better machine because its a DS.
I hope that answers your questions.