What type of dart do I have?

My first 1965 Form S 4 speed did have a 8 3/4 in it in 1974.....kinda early to be swapped out.
A lot of them were swapped out the first year. It was fairly easy to break a 7 1/4 with a 273 4bbl. 4 speed. Chrysler got tired of warrantying them, so swapped them with the 8 3/4.