I seem to remember a rumour during GWI that one of the RNs air defence
ships apparently managed to detect F-117As using some form of '50s long
wave radar.

No rumor, fact. Stealth is not invisible to all frequiencies. Some will detect
at longer ranges than others. Understanding radar therory and a close reading
of Aviation week will confirm the rumor. During DS the Hummers kept track of
the 117's for the Airfarce. What radars were destroyed by the snake eaters on
the opening salvo of DS?

Sparky