You need the whole beam in the car before you fit the diff, well it's the easiest way as you need to pry the diff down to tighten the front two diff mount bolts as they sit directly over the top of the two countersunk bolts (make sure they are proper flush too as they touch the diff mount bolts.

Your second to last picture, just above the brass coloured insert the casting thats 90 degree anticlockwise has to be cut off as it will fowl the exhaust system - most do both sides

Don't worry these are tight as fuck to get in, i had to shave the starting threads on the top right silver bolt as it was just a couple of mm out of line but caused massive issues and purely wouldn't go in.