Tip on installing the gears into the diff. Install the large side gears first. Coat in gear oil and be sure that, if there is an oil groove near the washer/shim, it faces the gear.
Next, with the large hole in the diff pointing up, put the first small pinion gear at the 12:00 position on top of the teeth of the side gears.
Then rotate both side gears in the same direction to place the pinion gear at the bottom or 6:00 position inside the diff case near the small hole, and place pinion #2 on top/12:00 of the side gears.
If you look closely you can see both pinion gears at 6 and 12 o'clock.
Then, to get the gears into position, rotate the side gears the same direction to get the pinions at the 3 and 9 o'clock positions. If you didn't keep the concave shims with the pinions, slip them into place now. The holes should line up easily with the shaft holes.
If you are doing a front diff, inset the pinion shaft and pin only. If a rear, you'll need to put in the axles, c-clips, and then the block and shaft/pin.
That's how I did it anyway!