Great post, thanks for this. As most people probably know by now, Flygvapnet did not mess around when exercising attack missions, neither with Viggen nor with Lansen. They'd often fly exercises in pitch darkness (heard once per week at some point during the '80s or '90s), and some of those times they'd be in complete radio silence for the entire flight, so that really great idea about a light hidden by the speed brakes definitely wasn't for show.
Here's a fantastic video showing some low-level Lansen flying. Watch the whole thing, not just at my timestamp. Crazy.