I'm running the same build, with a G4600T and a dual slot GTX 1050 Ti.
Both CPU and GPU passively cooled.
The whole build is powered by a single 12V AC adapter.
By using a singe-slot GTX 1050 Ti, I figured you could go down to around 3L, that is with an external adapter.
You could certainly lower the volume by using a short GPU such as the GT 1030.