2 vs 4 engines
The way i understood it, the 4 engine layout has 2 advantages.
1 - could spread the weight of the engines over the a larger section of the wing, hence making the wing lighter to construct and
2- in the advent of engine failure at V1 you only lost 25% of the thrust not 50%. I know the climb gradient required is larger, but the net result was you put smaller engines on.
A small ps on the CR story, i like the theory of energy 'recovery' as u smooth out the helical flow, kinda like stators behind the N1 fan.