As far as the case goes, if it can fit one, it can fit 2... if it fits the 1st one, it must be wide enough.... if it fits the MoBo, it must be deep enough.
234.8 x 127.6 x 340.6 mm (H x W x D) is not that small. ITX cases are smaller and SLI is done there; also remember that two 970s have a TDP comparable to a single 390x
Looking at the MSI site, and there's little info to be gained there
Here ya go... this is just an example, I don't like the limited offerings on some components
http://www.pcspecialist.co.uk/computers/intel-skylake-pc/
-Case offerings ranged from £29 to £48, I went £39
-Intel i5 6600K
-16GB Hyper X 2133
-GTX 970
-2TB Seagate SSHD w/ build in SSD
24X DVD Writer
-750 watt PSU
-Win 10 - 64
£830.83 ex VAT
£997.00 inc VAT Free Standard UK Delivery on all Orders
-- or on finance --
£30.48 p/m