Loosen both, I insert a pry bar between the timing cover and the generator bracket, pry up till the belt is barely snug. As you tighten the nut the belt will cinch up a bit. Repeat for the fan.
As a followup to thunderbirdesq's info here's what I do. Engine is an 8BA with wide belt set up and alternator but the principle is the same.
1. Loosen the 3 bolts in the first photo.
2.Slide handle of a ball peen hammer under cast iron fan pulley bracket so that the end of the handle just rests under the fan carrier bracket. The part of the handle closer to the hammer head will rest on the top raised part of the driver side water pump. Photos 2 and 3.
3. Push down on the head of the ball peen hamer so as to raise the cast iron fan bracket carrier upward.... and with the other hand snug up the big center nut shown in first photo.
4. Place a piece of protective hose on the tip of a long screwdriver. Can be either round or square shank. Slide the screw driver blade under the fan assembly so the tip with the platic hose rests between the timing cover and the block.Photo 4.
5.Making sure screwdriver blade is positioned ONLY under the generator bracket (mine is aluminum) pull upward on the SD handle so as to move the gen upward while at the same time snugging up one the bolt nearest you.
6. Then tighten up all three bolts. You may have to do this a few times to get the "knack of it." Be sure and remove all tools BEFORE starting engine!