First, check the balance of the rear tires, they can sometimes set up a shake that transfers to the front end.
Are all four tires the same make? Some brands are just incompatible.
The new front bushings on the inner A-frame ends, are they Ford or aftermarket? Some are too soft, allowing movement. Then again, some are too hard, causing flex somewhere else.
Finally, get a buddy to drive beside you and watch what's happening when it shakes.