I don't have much info other than production numbers on 69 sprints, (Ihave a 69 sprint 3-speed manual) but the 300 trans was the original transmission for the 69 sprints, though you could option for a turbo 400. As for info I wish you luck in your search as I had a 67 300 rebuilt about 10 years ago, and it was next to imposssible to find anyone that even knew what it was then.
Jeff