Re Tony's post, I think Alfred E Davies and Son of Northampton built similar small instruments in the mid-20th century. The concept was that of a limited number of extended ranks of contrasting tonalities which could be extended using couplers. Somewhere I have example stop lists, unless they have got lost during life's travels. They also marketed electronic organs under the name "Gregorian" which used a similar system. These were designed originally by the late Peter Walker who founded the QUAD high--end audio firm, famous for its amplifiers and electrostatic loudspeakers. He was an amateur musician who played the flute I think, though not the organ as far as I am aware. The Gregorian electronics did not have much of a reputation though, even by the poor standards of the day.