The first thing that popped into my mind was: Why? What advatage or feature is there on a full ATX board that cannot be found on a mATX board?
Looking at the adapter that comes with the Silverstone unit I think it won't work or at least it's very tight.
If you replace the PSU bracket of the Lian Li case with a custom one, there's a good chance it will fit.
The Silverstone PSU is not the best unit out there. If you do make a custom bracket (or have one made for you), you should take a look at the Silverstone SS-350TGM
. When you put it on it's side with the fan ponting towards the mainboard, it's as tall as standard ATX PSU, but only 63.5mm wide, compared to 150mm for a ATX unit. That leaves plenty of room for the mainboard. I think the Seasonic 350W unit won't deliver significantly less power than the Silverstone (FSP sourced) 450W unit.
If you list your planned components you could get an estimate for power draw. If you already have them, you could use a kill-a-watt and check yourself.