Is it possible to fit a 240mm MLC into the S1?
Yes it will, you can build the Ghost S1 as tall as you want.
With the 240mm version being 68mm thick, this does mean you will have to use 2 tophats, a large and a small one.
But will it look nice? That is up to you to decide.
Below I'll attach the dimensions of both the EK-MLC (240mm) and the Loque Ghost S1:
It's too difficult to make a custom loop since there is no suitable water sink and pump module for SFF cases, even though there is some room when the original GPU heatsink is replaced by a water block.
Damn right it's hard!
However it is doable, you don't
need a reservoir, of course it is optimal because of turbulence but as long as you have taken all the air out of the loop it will work.
I believe JayzTwoCents made a video building a dual 240mm system in the Loque Ghost S1.
Edit: Found the
video!
In the video, I see he used a Swiftech Apogee II which is a CPU/Pump combo.