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Urethane bushings are the only way to go, available for our vans up to year '08---nothing so far yet for the newer style radius arm mounting arrangement. For models '07 and earlier I'd use Energy Suspension #4.7107R (red color).
I'd also recommend urethane axle pivot and sway bar bushings too---all also available from Energy Suspension. I purchased mine from a local Jeg's outlet---they're but about a mile from me!
I need to change the radius rod bushings. My friend, who is a front-end guy likes rubber bushings over urethane. Is he crazy?
Many people, including FORD engineers, like the suspension compliance provided by OEM synthetic rubber bushings.
IMO most polyurethane replacement bushings are advertised to improve performance by substantially stiffening suspension compliance. This may be fine cornering on the race track, but often tends to provide a jittery ride in the real world. These bushings are designed to insulate passengers & cargo from routine road shocks. If you replace OEM bushings with especially hard polyurethane you will increase the transmission of vibrations into the chassis. Since most Econoline owners don't race their trucks they seldom take advantage of high-G benefits promised by polyurethane bushings.
However polyurethane does tend to outlast OEM bushings, primarily b/c most are so much stiffer. But there is a silver lining. For many applications polyurethane bushings are available in softer grades made to match more supple OEM compliance. So you can have your cake & eat it too.