Look at the two pictures below comparing the two. Notice the 69-72 support has a bucket spot welded to the support which the headlight fits into. The 67-68 support does not have this bucket, the headlight seats directly into the support. Plus, the headlights are in slightly different positions, so you can't simply remove the buckets to use the later support on earlier front end. Also, there is a row of weldnuts across the bottom of the 67-68 support for the lower splash pan that era truck uses.
