David I'll see if I can help without getting into any trouble. Things were winding down for the first generation Mustang. Ford was preparing for the launch of the new Mustang II platform, so no major changes were in store for the 73's. Most of the changes were appearance items. The 71-72 side stripes discussed were available as a separate option only when you ordered the decor group which included lower body side argent or black paint and molding, black grill, and trim rings and hub caps.
There was a Tutone hood option which gave you a non-functional NASA (Mach 1) hood with black or argent paint and the hood locks.
The Ram Air option was available on ANY 351 2bl equipped Mustang. Included was a NASA hood with black or argent paint, twist style hood locks, and "351 Ram Air" decals, just like you would see on a Mach 1. The air cleaner duct for this car is wrong. The 73 ram air housing had a 73 only part number because of the flexable hose that stapled to the duct. (A change was made in 74 to staple the flex hose to the plastic duct that ran under the battery and place a clamp on the air cleaner end-too late for the 73's)
Everything I have seen on the 71-73 Mustangs have indicated that the rear spoiler was only available on the Mach 1's and sportsroofs. The only time I have ever seen Ford production install rear spoilers on any vert (pre 1994) was in late 92 and 93 on some yellow, red and white Special Edition Fox Mustangs. There again things were winding down as Ford readied for the launch of the new 94 Mustang. There is a greater chance of it being a dealer installed item since there is no DSO call out on the door label. Either way you would need documentation or MCA would tear you up! I hope this has helped some.
