I did get the impression that the centre engine position of the Tristar was also a downside, as it prevented straightforward installation of larger engines as the model developed. I understand that the dimensions of the S-shaped inlet duct were the key issue here.
A lot of the Tristar (eg the S-duct) came from the Hawker Siddeley Trident, whose development ran down as the Tristar was building up. The senior engineers who moved across the Atlantic were a key part of the "brain drain" reports which were much publicised by government ministers in the late 1960s. The Autoland, FMS, and other sophisticated parts showed a number of examples from this background.
Hopefully all found the weather in Burbank (where the Tristar was designed, although assembled in Palmdale) a bit better than Hatfield.