I believe the tutone hood paint was only $18 on the Mach 1 because other mandatory content ( grill, mirrors) was already part of the Mach 1 package. $34 for the tutone paint on a convertible probably covered the cost of adding the grill and maybe the lower bodyside paint.
I have all the original ordering guides and salesman source guides for 71-73 Mustangs,and they spell out in excrutiating detail all the myriad differences in what was actually available depending on what combination of options and equipment was ordered. Some of the mandatory options as well as some of the restricted combinations are very confusing to understand why it is only available one way but not another. But if you think about each example long enough, it seems to make some sense once you figure out thier reasoning.
Another oddity most are unaware of is that many of the unique options listed only for a Cougar could be optioned on Mustang simply by putting the code on the order sheet, even if it wad not listed as an "official" Mustang option. Of course, it had to be things that would just bolt right on without any mods.
I ordered my car in late August of 1970, and I put two "Cougar" options on the order, and it came through with both of them without so much as a peep of anything from the factory: 4-way power seat, and automatic seat-back releases. I think the seatback releases were later added to the Mustang sheet.
Funny, two regular Mustang options I did order did NOT come through on the car: rear defrost and intermittent wipers.
It has been several years since I looked at those guides, but one thing I seem to remember clearly is that the tutone paint and the twist locks always came together, and niether one could be ordered seperately.
However, I have seen at least one factory publicity photo of a ram-air equipped fastback or mach 1 with hoodpins, "ram air" callouts, but WITHOUT the tutone paint. It may have the never-produced prototype for the 71 BOSS 302.
But, I have never seen a factory-produced car like that in person.