I am not going to answer your questions. But I will point you in the right direction. They are more complicated than they appear.
: is critical to a diesel and it varies with the year of the van and the wrong coolant will ruin your engine. Read here:
Power Steering Fluid
: Buy the owner's manual for your year van and follow what is listed in the manual. For instance my Bronco uses Ford Type F transmission fluid. I cannot remember what my van uses at the moment.
Front Differential Fluid
: So, you have a 4x4 conversion. What fluid was recommended for that differential in the vehicle for which the differential was originally intended. (You may be surprised by what you find. I had the rear differential rebuilt (broken pinion) in my wife's 2000 Dodge Dakota and the rebuilder suggested Valvoline 80w and when I asked him why not synthetic he said that rear differentials don't do well with synthetic. Go figure...)
May I ask you to post up what you find so that we all can learn?