Copied from "The Mustang Source" website: Hertz corporation ordered 1,001 of the G.T. 350s to offer as rentals. The side stripes read "G.T. 350H", but the cars became know as "Rent-a-Racers." Some cunning Mustang owners would rent the Shelbys, swap the motor with the motor in their Mustangs, and return them to Hertz. At $17 per day and 17 cents per mile, it was a good bargain for a Shelby engine. It was "uncool" to own a former rental car, so many of the cars were debadged after they were decommissioned. Thanks to the Shelby American Automobile Association, however, many of these cars have been found. More than 800 were made in black, and the other 200 or so were divided between red, green, blue, and white. Only the black models and a few white ones had stripes on the hood, but many owners added them to the other cars during restoration.
And this from "about.com": In all, only 1,001 of these fastbacks were built for Hertz in 1966. The makeup consisted of 999 units of the following colors: A majority in Raven Black with Gold (Bronze Powder) side and Le Mans racing stripes, 50 Candy Apple Red with side stripes, 50 Wimbledon White with side stripes (as well as several models with both side and Le Mans stripes), 50 Sapphire Blue models with side stripes, and 50 Ivy Green with side stripes. Two of the GT350H Mustangs were prototype models. Each of the cars was built in Los Angeles at the Shelby American Los Angeles airport facility.
I don't know how accurate these are. I'm sure some of our resident Mustang heads will post at some point.