Center Link Idler and steering Arm question

What you're probably seeing is a difference between years (68-72 vs. 73-76), not engine types. The relative position of the joints should be about the same so it may not be an issue with headers. If your choice of headers is very year specific then buy a set that matches the year range of the steering linkage you end up using.

See here for more info on steering linkage: http://www.bigblockdart.com/techpages/linkage.shtml