For those of you who may have a similar problem...I think I finally fixed my front-end clunk by replacing the upper ball joints. I replaced the tie-rods as well but most of the "clunkage" seemed to be caused by the ball joints. This site has some good info on how to do it yourself for those of you so inclined...
Autoclinix.com - Ford Crown Victoria / Mercury Grand Marquis Upper Ball Joint Replacement Instructions