OK so the pallet cooling plate is this bit of hardware. I got these on eBay (2 of them). I suspect I'll only use one, but I may end up using 2 instead. I'm starting off with ONE for now. But I have another in-reserve if needed. These cost about $212 each new, I got them for $100 ea. on Ebay. They're heavy, and very nicely made. There's enough room to mount all four of the BLF188XR (w6pql) Pallets with heat spreader's if I go the route of using just one of these coolers.
The reservoir will be 2 or 4 gallons I suspect. I haven't decided on what to use here yet. But it will probably be a metal barrel.
lastly the pump is a Swiftech MCP655 which cost between $76 and $110 depending on where you buy from. This particular one I'll use will cost $76 from Amazon Prime and it has a 5 speed adjustment on it.
These pumps are SUPER QUIET and they tend to last forever! They have 1/2" ID ports. It's important to NOT restrict in the inlet port so I'll be using 1/2" ID tubing for the INPUT and probably 3/8" ID tubing on the OUTLET (bound for the cooler plate).
I suspect this setup will be EXTREMELY QUIET! And that's the point of it. I can't stand loud fans whining while I'm trying to listen to a speaker or while I'm talking on a mike in the background.
The power supply I've built for this amp is fairly quiet, and this area will be even quieter. So all in all this should be a very quiet setup.