Here are some Cummins swap links for the 88-98 Chevy 4x4 trucks.

http://www.4btswaps.com/forum/showth...d-up-with-pics

http://www.cumminsforum.com/forum/cu...silverado.html

http://www.competitiondiesel.com/for...=chevy+cummins

Here's a Cummins swap on a truck like yours.

http://forum.73-87chevytrucks.com/sm...topic=15339.60

The existing crossmember on a 4x4 truck doesn't have to be removed, however you'll need to add an extra crossmember like the following. That crossmember is overkill. It doesn't need to be that hefty.