My father was a service rep. on the 1-11. He went on many delivery flights to the US with Braniff, Mohawk and AA aircraft and used to stay for a few days to see the new aircraft into service.
I don't know if training of US staff took place in the UK or US.
There was an occation when Braniff at Houston were having trouble changing engines and taking 2 days when the maintenance manual said 6-8 hours. A BAC team of 4 went to Houston to show them how, and did it in around 3 hours. Personally I've done it in 4-5 hours.
At the handover ceremony of the first Mohawk 1-11 at Hurn, the American boss said something like "I don't know how you can build such a wonderful aircraft in a bunch of old cow sheds".
More trivia if you want it.