I think that the 77 has more to do with who or how the car was ordered instead of the options on the car.
You are close....
Cars were built for different purposes. Some could be fleet cars, some could be dealer demos, some could be for car magazines/publicity/shows, some could be a truly special order car, like a special color paint, some could be lease cars or some were package cars.
Typically, one of these, or other, special purposes was indicated in the Sales Order (SO) number. The coding changed from year to year but most regular production SO numbers, tend to end in the 600000 range. The upper ranges (7**-8**-9**) are used to help indicate a special built or purpose car or, possibly, special shipping routing for a car.
So we're pretty safe in guessing the car in question was built for some reason outside of normal production. It's proably not that big of a deal. It could have been something as simple as an employee lease car.
I have several 68 tags with 'special' SO numbers but I do not know what 77* stands for. Check the broadcast sheet, if possible, for hints on why it got a special SO number. You may find some sort of sales code.
By the way....is the car in question white over white?