The GTO came out in 1962 but Ferrari had used the lip spoiler in 1961 on the 246 Dino mid-engine sports-prototype, and surely nobody could have imagined that was to prevent the ingress of exhaust fumes...........on an open car!
I remember reading press reports at the time the 1961 246 Dino sports racer was unveiled, no-one back then seemed to be in any doubt about the purpose of that raised lip, what we'd call a spoiler today, and I'm sure that someone at Jaguar must have been an Autosport reader and seen the same write-up that I did. Is it possible that Sayer was in love with the shape he'd created, and didn't want its purity of form spoiled with add-ons?