The message above left me feeling rather like someone who is trying to assemble a jigsaw with most of the pieces missing. . . . it might be edifying and useful for the rest of us (wallowing in a sea of darkness
:-) There are times when perhaps a nebulous darkness is preferable to the sharp detail illuminated by a spotlight . . .
From personal experience, for instance playing De Grigny with Grand Tierce on the pedal line which is perfectly pure and in tune with notes in the manuals when Meantone is used, the effect is so beautifully pure, calm and expressive of peace that perhaps whilst I can understand to some extent the point of view that Professor Peter Williams is coming from the reality is that I certainly would not describe it as a "cul-de-sac of a subject".
From my experience in "untuning" pianos and the sublime emotional impact that performances on unequal temperament can have in contrast to performances in equal temperament, the universal adoption of equal detuning of pure intervals has robbed a lot of classical music a dimension of interest.
Accordingly, it is important to be aware of the possibility of the existence of evidence of unequal temperaments and the message of BIOS of the 1970s was that even learned professionals might then still have been on the learning curve and in view of the limited uptake of temperament exploitation I wonder if this remains the case.
Questa's organ and playing are profound on the CDs but I'm not experienced enough to put my finger onto temperaments that I hear: there is always an interaction with the repertoire and the effect of temperament can be one of tonality rather than undue ear tweaking. At St Maximin and Albi, for instance, the effect is simply a "rawness" that excites.
Recently I have been trying early Italian repertoire on a Meantone tuned chamber instrument, the effects always being smoothly pure rather than ear-tweaking.
Without knowing the intimacies of Questa's repertoire I can't yet aurally measure the sweetness of the sound of his instrument to be able to be certain whether the photographs indicate exploitation of temperament of which I know him to have been aware.
Whatever the particular details are of what Questa was doing, the construction of a reasonably extensive pipe organ which could travel for concerts and in particular using wood less fragile than metal for the pipes is of significant interest in encouraging and promoting enthusiasm for organs more widely and the CDs are interesting to hear the sort of tonalities that he used. His musicological erudition was also significant.