Howie..those don't appear to be Mustang belts in the box...
I will dig out the paper work but shoulder belts were a option.If they were std factory stuff it wasn't until 1970.I have probably had at least 30 67/68 Mustangs and they didn't have them.My friends 69 SCJ Mach I doesn't have them either and the car has been in his family since 72..
I don't believe they were a option till 1968,same goes for headrests..
I will dig through some paper work
The belts in the box are not Ford belts.
They are from some spider web company that I have forgot who.
They where for BB to show him that it is not a big deal to put 3 point seat belts in his car.
This was the law beginning Jan 68
Standard 208
"Passenger Cars (Effective 1-1-68)
Lap or lap and shoulder seat belt assemblies for each designated seating position. Except in convertibles, lap and shoulder seat belt assemblies are required in each front outboard seating position."
I just know that my FB had the buckle down shoulder cross belts.
Still have the clips on the roof.
Even the most iconic 68 FB of all time, (excluding mine of course
)
LT Bullitt's green thing, you can see the clip that holds the belt up on the roof.