Yes I "HYC" the holes with a somewhat cranky and not much used super-computer.
the plates are indeed relatively thin, and there is a good reason for that. in order to keep the flow velosity right up there, even with the most puny of pumps emaginable, the block volume needs to be held at bay, though the ratio between the effective surface-area and the volume, is way up there.
To design the block to make the pumps life easy... that is not what the block is there for, sucking heat out of the CPU is what the block needs to wory about. Let the pump worry about getting the liquid through the block.
"If it can't do that, don't go open up the block.... get a stronger pump...." is what I always said
flow rate.... well
this is with 1000mm of lift.... 3 feet
which equates to about 169 GPH effective flow.