The most used kit has a new style crankshaft cam belt gear with skirts on the sides to guide the belt, along with a new tensioner setup. There is also a full mod kit that is only needed on some engines that has a new injection pump bracket as well and costs much more.
Which one may be needed depends on chassis/engine nubers I believe. Or it may just have been a bad belt. Can you get in to look at the broken one yet?