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Hi birdman., welcome..!
I think that's it (4")..! Keep in mind that's a lot of strain due to the drop. A 6" drop may not be safe.
I think I'd look into the "weld-on" riser for the axle end of the track-bar as well. (instead of/or in addition to, pitman arm/trac-bar drop bracket))
The goal is to get the track-bar & drag-link close to parallel.