Peter, perhaps consider whether there might be some pincushion distortion in the original of the image referred to by Bill and, if so, try correcting that before correcting the verticals.
Philip
Thank you.
If it were mine I would prefer the ends of the Quire Stalls to be 90 degrees vertical.
It does look like the floor is on a slight slope - in might be possible to make it appear less: again, if it were mine I would have a go at achieving that.
Re lens distortion (barrel / pincushion) - if you used an EF24 - 105L at the wide end, I note that lens has barrelling from 24mm to about 40mm, which doesn't seem to explain the way the floor looks to my eye.
Anyway it's a great photo and from what I can see in the small image that you posted, the PP is excellent: there will be differences of opinion as to how far we go to 'correct' the natural flaws in old Architecture - I tend to want to make it look 'nice' at he expense of making it an 'historic record' - that is unless the purpose of the image is a forensic, historic record, for example for insurance purposes, etc.
Thanks again.
WW
BTW - thanks for the links that you provide: I read them.
Bill