Pretty much yes. The big hole goes around the rebar and the wire goes through the top hole. As for how your going to do it i dont know. We usually just put a 2 gang mudring (essentially just a covered hole in the drywall) instead of an actual 2 gang box. Could try to get rid of that box by cutting it and sliding it up the rebar then put something like this in. https://www.amazon.com/dp/B000GAQB0W/ref=cm_sw_r_apan_i_SNB3QC2ZXQ25X7XCHDYM