'91 K1500....Few Questions.

Good afternoon gentlemen. My dad recently acquired a 1991 Silverado that has been in the family since new. Basic run down: Regular cab, longbed, 305, Auto, 4WD. 99K miles(no typo)

I will have the owner's manual soon, but I had a few questions...

What axles did GM use front and rear? How do I determine the gear ratio and if it has a posi? Will 75W-90 synthetic work well?

Dex/Merc in the tranmission?

Maxlife Dex/Merc in the transfer case?

Maxlife power steering fluid?

I will be using the grease gun, and replacing the PCV valve, air & fuel filter soon. Does the TBI system need any special attention? I'll get around to the ignition components.

Pardon the newb questions... I am familiar with blue ovals. Feel free to point out any other areas that need to be checked out. Thanks in advance!