There are two different styles of radius arm bushings for the 2wd trucks. I'm not 100% positive, but I am pretty sure, that the F100/F250 uses one type, and the F350 uses the other.
The lighter duty trucks use radius arm bushings that fit into each other, one is a "male" and one is a "female", so to speak.
The F350 uses a different type, and both of them are "male". The reason for this is the frame mount for the radius arm is thicker than on the lighter duty trucks.
Anyways, here's a set of them on eBay, for your F350, if you can't find them locally. If nothing else, it gives you a part #
HB1047K to use in your search at the parts stores.
ebay link