1970 Boss 351 Mustang barn find.....were any made?

[SS4Real]

I need help on a Mustang question from somebody who really knows exceptions in the Mustang world. While I realize most barn finds are not that exceptional, I stumbled upon a car today that really intrigues me. Visiting a shop today out in the country, I met the owner who had a picture of a Boss 429 Mustang on the wall. When I asked him if he was into Muscle Cars, he mentioned he had a few Mustangs and took me to another garage when he uncovered what he claims is an original 1970 Boss 351 Mustang with the Cleveland engine. The car was part of a limited run of 10 Mustangs as a follow on to the Boss 302 Trans Am racing program as engine displacement increases were being discussed. He has owned the car for 33 years (bought it less than a year old) and has had it stored for years. It's got the original drive train and is Grabber Orange (Competition Orange) in color. The car never made it to the Ford racing conversion center so it looks pretty stock to me. My question is did Ford ever make these 10 limited run 1970 Boss 351's? The owner claims he has documentation but since this was my first visit and I wasn't there to discuss muscle cars, I did not feel like it was the right time to pepper him with questions. If I can substantiate that a limited run of these cars was made, I will go back and get pictures and numbers. By the way, his wife wants to sell the car so if its legitimate, I'm going to pursue this. Any one know anything about these?