First of all, there is no hot-glue involved, no 3D printing, no laser-cutting, cnc, expensive tools & stuff. A drill-press with a couple tipps to carve, sand and drill holes, something, suitable for aluminium and acrylic with something to cut the parts such as a saw would be quite usefull but now please read the "Second" paragraph.
Second, I assume you have enough imagination and skills to understand how I did some things/work without cnc, 3D print, etc, etc.. so don't ask "How did you set the drill for this or that.." or "Can I do this with..". I just said I assume you have enough knowledge to get the point, therefore you're able to understand that saying "This will reduce the flow by XYZ%.." or worse: "It's only XYZ% cooler under XYZ% load.." & stuff" is only up to you to fix it to your sole and only pleasure the way you want it. It's for a Raspberry Pie & stuff alike, not Google's server.
This thing is meant to be quite easy and funny to built, fewer pieces as possible and a production-made look ...as much as possible. Of course, if you have access to a CNC, 3D print, etc., go ahead & set the world afire.
So, you should be able to easely use a drill-press as a lathe or for miling, kinda.
Step 1: Hack the Pump.
The pump does'nt have to be very powerfull so a small submersible 1 to 3 watts @ 12 Vdc is perfect.
The square piece of acrylic is'nt drilled through (for the two mounting-screws of the pump) to avoid a possible leaking point. The thing from the pump itself mut be drilled twice (or more, if you want to over-do it) also they're tapered so the (had to file them until small enough) heads of the two screws won't interfer with the impeller . Just heat-up a screw and thread the two holes in the acrylic. In the 4 corners of the acrylic plate it need four holes for the 6/32 X "as-long-as-needed" assembly screws (they're not in the picture, not even installed on the 'completed' picture).
I cutted two pieces of aluminium pipe to make 'stand-offs', ...otherwise the pump inlet would be plugged..
Then make a rubber gasket...
The plate will be machined (drill-press with router tipps) to "seat" the gasket and also to set the 4 heads of the screws at the same "level" so they'll end-up flush, kinda. Reffer to the pc-paint drawing.
BTW, it took me over an hour to draw this so look at it carefully and for at least 5 minutes so my work won't be worthless. Even better: download the picture and set it as your desktop background.
Since the hole in the reservoir for the pump outlet was done, milling the square piece (reffer to the superb pc-paint image) off-setted them. After a major facepalm, I just cutted-off these cutes littles alum' pipes used for stand-offs on the pump enought to compensate...
Check this instructable (https://www.instructables.com/id/Milling-With-Drill-press/) if you love dangerous techniques...
Step 2: Reservoir
That's the tricky part. It's a piece from the post for rails or fence. It's 2" by 2" and I made it about 2.5" long. Check the picture in the intro.
There's also a hole for the pump outlet wich have to be aligned with the pump's outlet hole. I'm using sorft tubing so it's tight at the pump and self-sealed at the reservoir. (Pipe is not on pictures).
Another hole must be done to pass the power cable from the pump, but I'll wait before doing it, you will see why later.
Step 3: The Manifolds and Radiator
First, make another gasket.
The aluminium radiator is salvaged stuff I had from who knows where since I don't know so... Anyway, I had to cut-off two rows of fins on either sides & flat-out the two surfaces with my super drill-press miling-rig (caveman edition). I used a bit made for a router.
Then drilled the fins to fit the pipes (in aluminium) going between the 1rst and 2nd manifold through the fins. Thermal paiste will be added between the pipes and the fins to improve heat transfer. The hole in the midle of the flat surface is just a pre-hole (ok, it was from a previous concept but it'll be used for..) ...for the passage of the coolant between the 2nd manifold to the reservoir. Also four holes in the corners for the (not in the picture) four mounting-screws.
For the manifolds, I cutted & kinda-machined two blocks out of acrylic and drilled them to create ways for the coolant.
I did one manifold at a time & drilled the holes for the pipes while using the radiator as a guide. Of course, two threaded holes for the (not in the picture) mounting-screws must be done before the drilling of the passages for the coolant and for the pipes in order to secure the manifold to the rad' to then drill the holes for the 4 pipes... got it?
The 2nd manifold coolant port to the reservoir is'nt drilled yet and a small groove for an o-ring will be made. SO the hole from the previous concept is'nt a problem. Both manifolds are to be held in place by the (not in the picture) four mounting screws on the final assembly. If you look close you will see the threads for them (in the manifolds), it's used instead of nuts for the (not in th... ok, you got it..) four mounting screws.
All joints will have an o-ring compressed between the manifold and the fins... or not, I'll super-glue them, I'm lazy.
Now all that's left is to make a hole to pass the power-cable from the pump but before I have to choose if I set it up or on the side with little stand-offs, if a fan must be added, maybe a little LED in the reservoir... and install these four mounting-screws (not in the picture).
I'll also post another instructable about the water-blocks for the Rasp' stack. Well, a two units stack... to begin with..
I hope it was clear enough but, like I said in "Second"..
Have fun and you should listen to Pink Floyd "Atom Heart Mother" while working.