clunking noise from 2005 E450 front end

I had a clunk in my front end as well - it is due to the steering damper mounting setup. As the cross-link is pushed back and forth, it is pushed up and down by the damper, hitting the limits of the cross-link joints.
I minimized mine by rotating the connector on the cross-link up to align the damper with the direction of travel as much as possible.

To test if the damper is causing your problem, remove the damper and go for a short drive.

Ford's front end design is a disaster, IMO. It's a wonder it works at all.

And the design Tito mentions is terrible. Took Ford from 1992 to 2008 to get rid of it and go back to end links on the front sway bar. But old or new, Ford's OEM sway bars, front or rear, are inadequate for a Class C.
There aren't that many bushings. Axle to Engine Crossmember, Radius Arm to Chassis, Sway Bar to Axle, Sway Bar to Front Crossmember.
Have you jacked it up at the outer ends of the axles and shaken/pried for worn Ball Joints?

BuckBarker wrote:
I think you are right on track with the bushings. What do they look like? Mine completely dried up and crumbled out.

Perhaps. When I replaced my stock anti-sway bar I noticed the ends of the stock bar weren't anchored to anything. They just go through this hole in the frame with a bushing. They bushing may have come out leaving the end of the bar with metal on metal. I don't know if this is your problem, but it's worth looking at.

I think you are right on track with the bushings. What do they look like? Mine completely dried up and crumbled out.