Stuck Motor Mount Bolts

[maxb]

I'm starting the process of replacing the (very much in need of replacing) motor mounts on my 300td. Unfortunately I've gotten stymied on the very first step - loosening the 8mm allen bolt from the bottom...

The motor mount is so crushed that I think the bolt head might be sitting against the steel of the frame. I've attached a picture of the situation.

I read a bunch of other accounts of removing the bolts and it seemed like the process was to clean out the head of the bolt as much as possible, and hit the allen key into the bolt to make sure to get a good fit, and then use a breaker bar to put as much pressure on it as possible. All I ended up with is the head slowly rounding out (I stopped before it got too bad I think).

I rented an impact wrench from the local tool lending library, so I'm going to go back at it tomorrow morning, but I guess the question I have is: should I lift the engine enough for the bolt to not sit on top of the frame anymore?