Floppy,
Getting warmer.
The Series 3 Whirlwind had a Gnome (and arguably a much better cockpit for night-flying than the Wessex..), but the original Westland S55s had the same piston as the Sikorsky. And the non-canted tail-boom... ZZZzzz.
I remember reading in Pilot a year or so ago about a civvy Whirlwind operator - was it the ex-Queen's-Flight HCC12? - somewhere in England to the west of Berks. Perhaps that's who was operating that day.