Slunnie and Long Stroke are right about real experiences being required, I am hoping those will be forthcoming and help show how air movement in and out of a Disco engine bay relies heavily on a careful a pressure differential balance.

For instance putting aside turbo’s and intercooler requirements does wacking in a "forward facing scoop" located around halfway cause greater pressures inside the engine bay to the extent of reducing air flow through the radiator by raising inside pressure (because air inside can’t exit fast enough) and therefore vents are required either forward on bonnet (where inside to outside differential should be the highest) and or side mounted vents?

Alternatively does mounting exactly the "same scoop but in reverse" and a bit further back on bonnet towards screen and in higher pressure area allow a significant but manageable amount of extra fresh air to enter engine bay without raising engine bay pressure and having no effect on through radiator flow, hence no need for additional venting?

A frustrating subject.