One bolt is keeping me from being a happy man!

I need to take the cover off the differential to disconnect the inner end of the axleshaft from the differential. The top bolt of the cover is in a tight spot and I can't get a wrench or socked on it.

Am I going to have to drop the differential? If so,the back bolts holding up the differential I can get, but the forward two bolts holding it seem to come down from the top of a support beam and they are again giving me trouble to access.

any helpful hints?

__________________
Phil
1985 300TD, 180K
1980 240D. 335K