IAD-JNB on 1/21 is showing as an A330-300. It typically is that, however they sub in the older A340 (with old business seats) about 40% of the time.
call their US number and they will assign a seat no problem.
18007229675
I'm on the flight in May. Unfortunately it was switched to an A340 recently. I posted about that here. Looks like the A340 may become more common on the route, but it's still random
IAD - JNB fuel stop