ChrisH, as you have pretty much found out, you can step into a dark nasty mud hole when discussing what did and did not come on something. Whether on a forum that discusses what shape refrigerator handles from the 60's were or were not, or what the content was on our 71-73's....Look Out!!
You can't go by the salesroom brochures. Most of those were air brushed to death and were normally full of mistakes. Interior shots of a Sportsroof that clearly show coupe roof trim panels, 4sp cars with automatic brake pedal, etc. There are early versions of the 73 Facts Book that show chrome exhaust tips. They did not make it into production. Just as David posted, as far as Ford was concerned, the 73's were dead in the water. By early 72 Ford had already begun preparing for the new Mustang II launch They had already sunk money in the 73's they would never recover on newly mandated emissions and safety equipment such as the crash bumpers. So some De-contenting took place to save where they could. To us, saving 5 cents doesn't seem like that much, but when the "Suits" in the front office multiply that by a single day production, their eyes gloss over.
As far as the 71-72's, there just aren't any part numbers that exist to support the existence of a left side exhaust for a 2bl equipped 71-73. The three "H" pipes listed for the 351's were for R,M,and Q engines which had larger exhaust manifolds. The OE and replacement exhaust for 4bl Mach1's were one piece from the intermediate pipe to the tail pipes. The part numbers were unique to the 4bl versions because of locator tabs that were spot welded to the tail pipe end to fit in a slot in the chrome tip to align them so as to not be crooked.
As I posted earlier, the rear valence with cutouts was a popular over the counter item, Sales dept included. Even into the 80,s you could purchase the D1ZZ-6540544-B panel for $53.55. And if you wanted the Ford chrome tips to to install on a aftermarket exhaust, they were in the $30.00 range! All affordable.