[Gooserider]

I would not expect you to need a pump any different than the one you would use for a comparable loop using a heatercore. The concern is the volume of coolant through the blocks, not the volume the rad can pass.

If I were building something like this I would probably put a small / medium pump, like an Eheim 1250 or a Danner Mag 3 on each loop, and use the rad bottom tank as the input to each pump via a thick hose. Either skip the res entirely, or have the loops dump into the res and have that feed into the top of the rad. I wouldn't expect there to be enough flow resistance on the rad to be noticeable at any flow rate you would get with a WC pump. (Not scientific, but back when I used to work at a gas station, even with a garden hose it was hard to get enough flow to over flow a rad when flushing it.)

Gooserider