Model R7800 and a aftermarket directional antenna.

Ok, I pretty well got this figured out. I tried one antenna at a time to see if any were 2.4ghz specifically. The left most seems to be 2.4, the next one seemed to do 2.4 and 5ghz, the third was 2.4, and the last did nothing. So I just removed the 3rd antenna and hooked up my directional one. At the other building I tried each of the antennas on the network extender to see if one was better. It turns out the left most, or bottom depending on your orientation, had the strongest signal.

In the end I have 2.4 and 5ghz in building 1 and 2.4ghz beaming Internet to building 2. Building 2 also has 2.4 and 5ghz signal, but of course it will only be as fast as the 2.4ghz signal going to the extender.