quick question.

The 3rd members will swap housing to housing but there are some different pinion flanges. 7260 U-joints (2 1/8") 7290 U-joints (2 5/8") are the most common but there are some others that came on Imperials and full size C-bodies with the C/V joint type driveshaft that are different as well as some early truck varieties. Between 3rd member housings (and therefore pinion shafts) there are coarse and fine splines in most versions too. Some will interchange but some won't so it's best to get a 3rd member with the same exact u-joint size so you don't run into compatibility problems. There are conversion u-joints available in some sizes but I always thought those were mickey mouse.