If the car has an export DSO and the additional support welded and chalked on the firewall. You would have no problem.
If not be prepared to support the idea that it was available (not just made during the production year but an advertisement for across the counter sales)from the year of production would be expected. You will often find some resistance for performance related accessories
Weren't many of the Shelby American bolt-on parts available over the counter from Ford? Granted, there may not be documentation that they came with a particular car, but the same thing can be said for other bolt on dealer options. There is a point where some people over-accessorize their cars at all levels, but a few of them done well shouldn't be a significant deduction, should it?
You may have misunderstood what I wrote. For the "normal over the counter accessories" most judges would not require you to have a sales slip showing that your particular car had that item - currently.
Instead you would be expected to produce a Ford, Rotunda or Autolite part number and some way to prove that that part was available as a accessory the same year as your car. A sales add is normally the best at this.
Of course this could change in the future if MCA or other organizations started requiring Marti reports (or had them pulled for every car on the field). The Shelby did basically the same years ago when they made all the Shelby records public
Yes some cars have been accessorized to a very high level (have seen cars lose points for this) and owners need to understand that they are only increasing the possibility of losing points in doing so.
Of course any option that would have voided a warranty or not been allowed due to state or federal laws will typically not be accepted even with the documentation mentioned
The judging sheets are broken into 5 main categories, Interior, Exterior, Trunk, Engine Compartment and Undercarriage. At the end of each of these categories is a 5 point item for other items not proper or original, including over-use of Ford accessories. The purpose of this section is the keep owners honest and not go out and build a car that Ford possibly never would have sold new... for example: attaching all K code engine components to a '66 C code.
1 or 2 accessories here and there are ok, but just keep them tasteful and "believable".