'65 Formula S with "factory" 727 and 8 3/4?

I have not seen an option code that specified a 8.75 rear end. I know rumors abound that back then a buyer could order a HD rear end, but I don't know what the option code was.
I currently own a 65 and 2 66's, all factory 4 speed F/S cars and all came from the factory with 7 1/4" rear ends. Both 66's had 71/4 sure grip rears.