If the arrangement tab is not visible under OS X, it means that your system does not see one of the two DVI monitors. Are you connecting both to your GTX 970? The G1 has a non-standard port layout with its dual DVI ports. Are you restricted to DVI on both monitors? Do you happen to have an HDMI or DP to DVI adapter? My suspicion is that both DVIs will not work simultaneously due to the custom PCB on the G1 edition of your 970.
Alternatively, you can research how to use your built in HD4600 and your 970 simultaneously. It looks like your Asus H97M-E has a DVI port on it? You could run one monitor off the 970 and one off the HD4600.