Don't know anything about the crown Vic, but some things to look at. A car that is ten or so years old will likely need overhauled. Steering, suspension and brake parts will probably need replaced. If you have a line on a clip locally I would find someone who knows what to look for, inspect the clip, and add up the costs before laying down your cash.
Advantages of buying a good kit should include:
A customer service hotline, usually from a manufacturer.
Detailed instructions and templates.
No rework or part replacement.
Look into these things, no matter which path you take.
