Don’t wish to seem pedantic or over critical because I’m a great admirer of the material you post. But…the AEC Mercury range never used the 7.7 litre engine. They had AEC’s AV470 engine, which was a very different design in many features to the pre-WW2 designed AEC 7.7 engine. It has been a common error for many years to use 7.7 as the term for the 470, which was in fact closer to 7.7 litres swept volume at 7.68 litres than the pre-War “7.7” which was 7.58 litres.
AEC 7.7 litre engine range, introduced in 1934, dry liner, 105mm bore x 146mm stroke, bhp 95 - 115 @ 1800 rpm
AEC AV470 engine range, introduced in 1953, wet liner, 112mm bore x 130mm stroke, bhp 105 - 140, 1800 to 2400 rpm