This may be veering slightly away from the original question, but I wonder if David, (or anyone else), knows anymore about the Walker/Compton connection?
I've heard it said before that Compton more or less kept Walker alive and kicking by whatever means, and there was mention of sub-contract work at a time when church organ-building was in the doldrums. The boom years for the theatre organ were, of course, between 1924 or so and 1945; only a twenty year period, but a big enough market to keep Compton, Wurlitzer, H,N &B (Christie) very busy indeed. Presumably, the Compton works at Acton would not suddenly burst on the scene as a fully fledged manufacturing plant, and the build up must have been relatively gradual, even allowing for the financial backing of a wealthy individual. Compton's first premises in London were the former August Gern works of course; Acton coming later.
I haven't surveyed the output of any of the firms involved in the building of cinema organs/extension organs, but I would assume that these instruments reached a peak between 1930 and 1939 (the start of WWII) and then revived again, (purely as church organs) between 1945 and perhaps 1955 or so; 1954 being the counter-reaction year with the building of the Festival Hall instrument, which of course, caused a saesmic shift in organ-building and tonal-design.
It's interesting how two adjacent counties should contain good examples from the end of one era to the start of the next: the Walker organ at Buckfast (Devon) and the Compton organ at Downside (Somerset).