My guess is that the 7 blade fan would show a nominal improvement over the 5 blade.
That seems to be a reasonable guess.
The MP 5-blade has more pitch than the ...215 18" 7 blade.
The blade is wider, approx 3.8" vs. 4.6"
Presumably the 18.5" ..216 potentially can move a little bit more air than the 18" 215. That can only occur if the surface area of the core is exposed to the fan's airflow.
IMO the big advantages to the early fans is the extra clearance with the round top radiators.
The mopar kit was put together for, supposedly, max cooling with minimal drag. It may also have been based on "the tooling we still have laying around."
That also seems to be a reasonable guess. It would have been a lot harder getting a pre-70 style fan back into production than using something more current at the time.
