Transposition in seventeenth century English organ accompaniments and the transposing organ

This brave fellow tried to understand early organ music in English Cathedrals. I live in England, sing tenor, play the organ, have visited all but 2 Cathedrals, regularly email organists, masters of choristers, researchers, organ builders. We in England - at great and pains-taking expense - are just beginning to see a little beyond what JBC wrote back in 1974. Basically, from 1460s-1640s, the ancient Britons sang to an organ which had C/F as the lowest note (sounding around 100Hz, the bottom note of a rank of 5ft open flues). We have music going back to earlier days (where folk used a C-based organ and an F-based organ) and this is enough to drive us mad, let alone the stout visiting guy JBC. The lad did damn well. Still worth a read. Only serious error is he thought the case at King's Cambridge was 1605-6 original; it's half a century later.