But wait...........Front crossmember part numbers are found thanks to Eric's part number database http://www.coolcats.net/tech/reference/'83-'85 - E5SZ-5025-A '86 - E6SZ-5025-A'87-'88 - E7SZ-5025-ABrent
As for factory K members, if your R&P is still utilizing the original(to your year) R&P bushings it would be best to stick with the '78-9/'84 K member.Also '78-'80 K members the rear inner bolts are closer together than on the later 81-04 cars, which can be rectified to use the later and lighter K members. So.'78-'80 direct bolt in.'81-'9/84 require rear inner bolt location change to fit.(mod car not K)10/84-'88 same inner bolt location mod and use a different R&P sleeved bolt.'89-'93 I4 Ks are the same as 10/84-'88 Ks'89-'93 V8 Ks have a 1" wider track width. These can be identified by the welded in upper spring mount vs the stamped hole with triangles.