The way I have done it on that position is to remove the transmission mount and drop the back end of the tranny down as far as you can. Then I have like a 3' or 4' long 3/8" extension that I have always been successful in removing the top bolt. You may need to adapt it to a 1/2" breaker bar. Make sure you clean the allen head out real good and firmly seat the socket down in it.
I purchased this 85 300D wagon engine one time that the mechanic tried to use a torch to cut off the upper bolt and caught the inside of the car on fire
and totaled the car out.