I added a second extruder on my Ender-3 but with it, I had a new problem. I needed to put somewhere a second spool of filament. So first I created a spool holder and now, I created an angled holder for Nema 17. I didn't want to start from zero, so I did a remix of another one I remixed before.
If you need to fix the extruder on the place, you can use a prepared hole for M3x16-18 screw with a nut. ;)