Thanks for all the replies. I'd love to hear further Belfast stories, so please keep them coming. Sad that the one in Oz is no longer flying.
"Four Vanguard engines on an aircraft the size of the Belfast:" well, yes, the engines always looked a bit inadequate in size for the sheer bulk of the aircraft (ditto the C-133 in my view too, interestingly). And my Ian Allan "Military aircraft of the world" from 1973 (price £1.95 for a-admittedly not very large-hardback book!) gives a max cruising speed of only 352 mph for the Belfast. Whereas my Ian Allan "Civil aircraft of the world," 1974 (£2.75, for same size of hardback book as the Mil version above-that's how bad inflation was in those days) gives a max cruising speed of 425 mph for the Vanguard.
The books also tell me that the Tynes on the Belfast were 5730eshp and the aircraft had a max gross weight of 230,000 lb; whereas the Vanguard had 5545ehp engines and a gross max weight of 183,500 lb. The figures speak for themselves and bear out what is said above.