what kind of bushings are you thinking about using? even though the ball joints dont move in the traditional manner of say a long arm/ short arm type suspension, they will still need to handle stress from all different angles.
a strong sealed bearing would be the only acceptable route in my opinion (such as wheel bearings or on upper strut mounting plates) but it would have to be very heavy duty. unlikely to find one small enough. Just a rubber bushing with a metal sleeve might be a bad idea. It will at least affect alignment not to mention what the stress will do to it.
i wouldnt touch the ball joints. ford uses some pretty beefy ball joints on the bigger trucks and they are a high failure rate item. imagine what that stress will do to rubber.
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