Just had the same issue on my 52 1/2 ton. same mount as you have. I put the jack under the engine and lifted until I could see the mount come off the cross member. Then I was able to force a deep well socket on to the bolt. Then I was able to get the ratchet on and it came apart. The clutch side was not so easy. Limited room between the clutch and brake support. I did use a big screw driver to push the mount down like a lever. Hope you get it off.
