20V waterline kit questions.

[Aram]

As I was gathering parts for the conversion it came to my attention that all the holes on the 20V engine were bigger than on the 16V.

Here 2 examples:







Having read a few topics on this matter there was also talk of a hybrid waterpump using the back of a 16V and the front of an 20V, but to make this fit the impeller blades need to be grinded down by 1mm.

All this makes me think the 20V waterpump pushes more water around than the 16V.
Toyota probably didn't do this without a reason but what is that reason?

And what is the consequense of putting the (possibly) restricting 16V parts on?