Rear differential question...

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Rear End Vibration Damper - That heavy bone shaped thing on the front of the rear end snout is the factory vibration damper. Each one is tuned to a frequency that corresponds with the factory gear ratio to cut down on noise, vibration, and harshness (NVH). Turns out the thing is no longer at the proper frequency if you changed the rear end gear ratio. Take it off and throw the bottom bone shaped part in the nearest trash can. Keep the top sheet metal part and reattach it to the rear end with some shorter bolts. This gives the pinion snubber something flat to hit against.

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I thought he was talking about the dog bone too until I read the last sentence of the question. I don't know what bushings you are reffering to. Its just a chunk of iron. In either case, chit-can it.
The 'dog bone' does have two rubber bushings. Ford is probably the only place to get replacements if yours need replacing.
Honestly though, I would just remove it. The metal sleeves in the bushings (of the dog bone) slide out pretty easily. You can remove and reuse the sleeves along with the stock bolts to remount the snubber smacker plate back onto the rear end. It'll look kinda funny with the two bolts hanging low. But it will do until you can get some shorter bolts.