I think the DHD you want is the one piece tail section. If it says DHD and is a two piece tail section then it may not be a big shaft DHD. I may have it backwards, I will try to look at mine and find out. One way to make sure is if you get one from a 3500 diesel, it is probably gonna be the Big one.
The DHD will handle tons of abuse, there are pullers putting down close to 1000HP through them.
One thing to remember is the 97 and older trucks have a different shifter than the 98+. 98+ the shifter is mounted to the body, the 97- it is mounted to the tranny, and I think it has a different shift pattern also. I also think the holes in the floor are different. Scott Vorhees did a 271 swap into his 97, he would be an excellent source.