Update December 2020: At the brackets' thing page, Psychicpotato reported that the X,Y numbers for the sensors should be negative, "EX: BLTouch is -43x, -9y". I have no way to verify this, as I'm not using the brackets; I had the dummy bracket installed in my printer; and now I've been unemployed for almost a year and haven't touched the printer; it's still in a box. Just thought I'd let you all know in case someone has hard trouble with auto-leveling settings.

Update May 23, 2019: I've updated the Autolevel Sensor Brackets for Z-19/Z-23 page with the X and Y numbers info for all sensors supported.
https://www.thingiverse.com/thing:3099237
NOTE: YOU MUST PRINT THE BRACKETS together with the Z-19, and use the dummy one if you have no auto-level sensor. The two "feet" (screw guides) on the left side are raised from the metal plate by a couple of millimeters, to make room for a sensor bracket attached there. If you don't have at least the dummy filling that gap, and you tighten the screws, chances are the Z-19 will break.

PLEASE SEE DAY-TO-DAY UPDATES AND REVISION NOTICES AT THE BOTTOM OF THIS PAGE, UNDER CURRENT STATUS AND REVISION NOTICES, RESPECTIVELY.

INTRO:
This is a printable replacement for the printing head housing (square, or rather cubic, metal housing) that comes stock with the Creality CR-10 and CR-10S, mini, Ender 2 and 3 and many other, if not all, Creality 3D printers.
It was inspired by the famous "OEM Fang Mod", and like the Fang Mod it allows better viewing of the printing in progress. But the Z-19 mod differs from the Fang Mod in many ways, some of them very important, such as improving the cooling by taking basic --but somewhat counter-intuitive-- rules of aerodynamics into account (read more about this below), and by improving mounting ruggedness.
Installation is pretty simple. No cutting, drilling or soldering are required; this mod uses the same fans and hot end as the original; it is a plug and play replacement for the metal housing. All you need is allen keys, and a cutter or razor blade to strip a loop of insulating tape, just to loosen the fan wires a bit.
Detailed installation instructions provided further below.

NOTE: If you DO want to upgrade your fans, then print my Z-23 mod, instead.
https://www.thingiverse.com/thing:3085235

Advantages:

• The Z-19 is meant to be an entry level modding fang thing, easy to print, then swap out the box and in the print, no cutting or soldering; no new parts to order; only some screws you'll need to replace. 11 hours of printing; optional painting; then 15~30 minutes installation.
• Weights a lot less than the original metal housing --even when printed with 100% infill
• Offers better view of the printing than the original metal box, much like the OEM Fang mod does.
• Unlike the OEM Fang mod, it Is compatible with the Micro-Swiss All Metal Hot End.
• Better mounting: uses the two original mounting screws AND the two screws for the hot end; plus it has multiple contact points against the back plate, for a very solid, non-shifty, non-vibrational attachment.
• I believe the Z-19 delivers better cooling than the original (metal) housing design; but I cannot make a categorical claim about this, as I don't have the equipment to verify it. Certainly much better cooling than the OEM Fang Mod.
• Includes finger-guards to protect the fans --and your fingers-- from each other
• Includes a hook for the extruder tube, so that it stays up straight
• Designed in Blender, painstakingly avoiding triangles (better than 90% quads), for smoothing subdivision -friendliness, and to be easy to work with and maintain.
• It prints as a single object --in one piece; no parts to assemble, except for the customizable bed leveling sensor holding brackets. (NOTE: You MUST print those, and if not using auto-leveling, then insert the "Dummy" bracket, or the Z-19 will break.)
• The STL file is a single, closed solid (a continuous, closed manifold), without cracks or holes, duplicated vertices, dangling edges, loose geometry, flipped normals, overlapping facets, inter-penetrations, or any such common mesh flaws. There is absolutely nothing for the slicer apps to plug, heal or fix.
• I've been told it looks cool. ;-)
  NEW AS OF REVISION 1.61:
• Allows swapping of a 40x40x20 mm muffin fan for the 40x40x10 original.
• Allows a customizable bracket to be inserted to hold an auto-bed-leveling (ABL) sensor.
• Four such brackets already provided in a separate STL file. One of them is a dummy bracket to fill the space under the Z-19 when no ABL is used. The other 3 brackets support the three most popular ABL sensors I know of:
  BLtouch
  https://www.reprap.me/bltouch.html
  TH3D's EZABL 18 mm
  TH3D's EZABL 12 mm
  https://www.th3dstudio.com/ezabl-kit/

(Note about the images: Not all pictures are of the latest revision. The four black and white that are together are from back at revision 1.0, for example. So, don't be alarmed if you notice discrepancies.)

And another NOTE: If you're looking to upgrade the model cooling blower to a 5015, I have something very similar to the Z-19, but which supports the bigger blower: I called it the "Z-23", and here's a link to it:
https://www.thingiverse.com/thing:3085235

Needless to say, if you like it, don't forget to Like it :-)
And if you make it, don't forget to Make it. ::-))

A big shout of thanks to makkuro, who cutom-made a text customizer for us, which I use to show the name and revision number whenever the revision changes. The custom customizer I'm talking about is here:
https://www.thingiverse.com/thing:3094095