Let me repeat, I am no expert. That said, the short answer regarding changes and fitment concerns is “few.” If memory serves me correctly, switching to a nine or eleven-bladed fan did not present any fitment issues, although the newer-style fans seem to sit closer to the radiator than with the five blades. Further complicating the fitment is attaching a fan shroud to improve air flow - if your original radiator or radiator support does not readily permit this. (Hint: 2x check those motor mounts and transmission mount to ensure against too much engine movement during severe braking or acceleration.)
Regarding the 400mm versus 420mm conundrum, I cannot speak with any authority as to whether an additional 20mm creates any any additional fitment issue/s. Sight unseen, after 50 years, radiators and radiator placements have a tendency to vary with each application. And . . . if your radiator has been re-cored or replaced, it is impossible to foresee how or by how much the radiator might differ from the original.
Regarding your post whether the highlighted parts would make for a complete upgrade, it appears that the answer is a guarded, “it depends.” If, for example, your vehicle has been in an accident, you might have unforeseen fitment issues. Likewise, not all parts, even new ones, are identical. But, if you are considering a wholesale R&R of the current cooling system, why not upgrade to a new water pump that accepts the eleven-blade fan?
Unless you are experiencing overheating or poor cooling issues, you might consider keeping what has worked for five decades, i.e., five blades. In fact, if your fan clutch is failing to engage, a simple fix might be to try shimming the clutch as mentioned in forum threads, or as a default position, locking the clutch by two lengthy bolts. Obviously, the latter solution is less desirable, considering additional noise and drag. However, it is probably far more common than some might think, considering the cooling issues it might prevent.
