OK this is a total rework for both fans on the Wanhao D9, as the existing cooling solution basically does nothing and is an embarrassment to engineering.
You'll need two 5015 style radial blowers, 24V. There are screw points for them that you can use, but they slot in tight enough you probably wont need them. If you do, then you might also need to use a tap on two of the holes to make proper M3, the thread is build into the model but orientation means it probably wont come out well. If using imperial then 1/8" would be best bet..
Print with the fan duct facing upwards (same as thingiview), and use support for the first couple of mm - looks like Cura doesnt have a setting to disable support above a certain layer height though, no idea why, but Repetier does. Check to make sure support is covering the entire relevant section of the base - might need to make sure that bridges are supported, again a function in Repetier but not one Cura has. Of course you can still print in Cura, maybe alter the support angle threshold to horizontal reduce waste. See pic for orientation and support in Repetier.
Suggest using thick walls, I printed on another printer with 0.6mm nozzle and did 1.2mm walls, relatively low infill. Infill is only required for designed in printed supports. Also maybe check solid infill threshold area setting, and reduce as necessary.
Once done, it should slot tightly over the entire extruder, and you'll then be able to screw it into place as per before. I designed this for my other printer to print, which tends to make walls etc about 0.2mm thicker than necessary, so I would be interested to hear how it works out for you. Remember to make sure that your print nozzle and block are perfectly aligned flat with the build plate underneath - if there is plastic getting in the way from this print (where the support zone is) you might need to lightly file it down.
Also, this model is actually a slight tweak of the one that I printed, I adjusted the airflow exit a couple of mm down. If you print it, again please let me know how it works out for you.
And yes, yes I do know this model is insanely, ludicrously, unnecessarily complex. That's how I roll.
Other D9 mods of mine:
Needs support for first 2mm or so, disable above this level