The June, 1985, Thomas Cook Continental Timetable shows the following possibilities:

Victoria dep. 8:15 to Dover, ferry to Oostende, Saphir to Cologne, change to sleeper/couchette/seats car on Holland-Wien Express, arriving at 8:00

Victoria dep. 9:15 to Dover, ferry to Oostende, change to sleeper/couchette/seats car to Vienna on the Ostende-Wien Express, arriving at 9:40

There are other, less convenient, connections (via Calais or Harwich/Hook of Holland or by changing trains in the middle of the night) but these are the best ones.