You should be able to use a line wrench, if it is timed properly. I have had some of those fittings which I couldn't get a standard line wrench to turn them well. I got tired of fighting some of them and bought a crow's foot line wrench. It let me use an extension so that I had the ratchet down away from the transmission. This gives more clearance from the frame.
I usually have to use a wrench to hold the adapter in the transmission from twisting.