The Ambassador was not particularly well received by BEA, the only airline to buy them new. Introduced in 1952, the 20 were all out of service by August 1958 and then took some years on the market to trickle down to secondary users.
The Munich accident was shortly befre their final withdrawl. I believe the charter flight to Belgrade and return used an Ambassador because there was no supply of jet fuel readily available at Belgrade so a Viscount could not be used.
Dan-Air did a daily sevice from Liverpool to Amsterdam with them in the 1960s. I recall the start-up each morning was accompanied by clouds of smoke, seemingly the sleeve-valve concept with radial engines allowed even more lubricating oil to seep down into the bottom cylinders than happened on other radials, which was then burned off in the initial seconds.