I've never seen J81 coded on the fender tag of a 1970 b-body convertible (I only follow the Plymouths though) and the 'saleman's pocket guide' and the 'dealership data' book don't mention wing availability at all (that I see).

What were the 'rules' for J81? Anybody got a tag with J81 on a convertible? Any factory info that talks about the wing?