Not all F-104s had downwards firing seats; only the XF-104s and early F-104As.
http://www.ejectionsite.com/f104seat.htm
One of Roly Beamont's memoirs has a sobering description of his briefing as the first non-US test pilot to fly the type. The briefing was interrupted by a cloud of smokeon the horizon, and the pilot failed to escape. Downwards firing seat in that one he said, IIRC.