I love the performance boost that headers provide, but they can be a real pain! You probably already know this, but not all headers are created equal. Some provide more clearance than others. I put a set of Dougs D453 on my 408 stroker and they worked very well. Only issue I had with installation was because I upgraded the torsion bars to a 1.03 so had to clearance some of the tubes. If I left the OE bars there would have been plenty of room. Also had to use a different starter, but the newer (smaller) starters are better than the old/larger reduction gear ones.
Just curious; did you find a set of OE performance manifolds for that engine that you're replacing the headers with?