The picture shows a trap oxidizer replacement pipe. In addition, the front exhaust pipe is also replaced by an oxidation catalyst/front pipe assembly and that is it. That is different from the 87 300D which gets the entire exhaust system replaced including a new muffler and a new center resonator. I believe the Catalyst replacement letter started in December 1996.
It is hard to say what price you should pay for it. In my opinion, a used SDL is usually overpriced when I compare it to other diesel models. But some days, I may buy one if the price is right for me. Just keep in mind that the rebuild engine is 8000 to 12000 dollar and a new head job is about $1500 - 2000.