I agree that it is a Reynolds 531 butted main triangle, based on the post size. However, I'm not convinced that it is late 1960s. Unless the head sticker is hiding some rivet holes, I'm inclined to think that it is a post boom model. I recall all the Falcon having riveted head badges through the early 1970s boom. Certainly, the decals are the post boom style and even the colour is the post boom Falcon team blue, though it may be a repaint with newer decals.