I looked for a cast iron CJ/PI tail housing when we built the C6 in the F-100. Like Eric said, found out they are impossible to find. We had a short cast iron pickup tailhousing but using it meant we would have to build a driveline with a slip in it. From experience I know driveline slips are a weak point. So we used a long aluminum tailhousing and bought a chromoly slip yoke. Despite my best efforts to break it, or anything else for that matter, it seems to be pretty tough.