This is a variation on the BMG Side Mount - 45° - 3030 HEVO by LazaroFilm. I like the 45° angle but wanted the motor and extruder to sit on top of the 2020 rail. Also, I am using multiple extruders in a row and I wanted to be able to move or detach them when necessary. So I moved the mounting bolts to the back of the rail.
The photo that shows 4 mounts are design variations with the 2020 mount by LazaroFilm to the right.
Also features a slot in the back to attach zip ties for cable management.