According to the catalogs, that wouldn't appear on a bike with this geometry until the 1986 model year. For whatever that's worth.
I have a maroon 84 or 85 720 and it has that cast bottom bracket.
It's been a while since I dug up the information. I believe the SN puts it made in 84 but the head badge puts it as an 85 model. I could be way mistaken.