Daimler also produced a bigger brother to the 2.5 litre V8 - the 4.5 litre unit used in the Daimler Majestic Major.
By all accounts it was a great unit and although it would never have been able to fit the MkII it was tried in the MkX wherein it gave performance superior to that of the XK-engined version.
However, I believe that Sir William Lyons was embarrassed that the Turner V8 outperformed the XK, and felt antipathy towards the V8 configuration for some reason best known to himself.
The sad thing is that engine might have made an enormous difference to the E-type, and the XJ6. It might not have looked on paper to have been as exotic as the twin cam XK, but would no doubt have plugged the gap brilliantly between the ageing XK 4.2 and the later V12, and would surely have appealed more to US buyers.
The engine had already been in production for some years. A missed opportunity, surely, especially as later on, in the Seventies, Jaguar did toy with a V8 version of the V12. However, the 60-degree V8 - a bad idea, according to those who know about these things - never achieved the necessary refinement.