With enough time and money, anything is possible. Obviously, it isn't a bolt in. The crown vic came with a 4.6L, so your 5.0/fox body motor mounts aren't going to work. I am not sure if the trans tunnel would have enough room for the larger C6, so cutting and patching may be required. And finally, I know the crown vic rear end is several inches wider than the fox body... this will require either a wider rear end or a creative wheel/tire combination to make up the difference. Those are some of the major challanges in my mind... obviously, all the usual stuff like gauges, fuel pump (assuming your 429 is carb) ect ect still apply.
An LTD might be easier, since they originally came with a 5.0.