Again looking at the shop manual you can see the fork fits into the grooved bit of the throw-out bearing that has a "lobe" shape. That keeps the bearing from spinning in the fork fingers. The fat flat face on the bearing is to the pressure plate and the grooved end is to the transmission. And, yes it will only go on the fork two ways. Sorta left and right from your description. At least as far as the "lobe" is concerned. If you have the bearing groove in the fork fingers you have it right. As long as the fat flat face is to the clutch. Think lever. You need the leverage to work against the spring. Only got one leg to work with. And you need a lot of spring to keep the clutch pressed together to move the truck. The end of the fork finger is the point on the lever that moves the bearing that compresses the spring. You need the point to stay in good shape. So you don't want the bearing to spin and wear those fork tips out. And that is what the "lobe" does. I hope this was helpful. Let us know how it goes.

Steve H