Ed,
If you have never visited "The Scale Firehouse", check it out. It is a website for emergency vehicle model builders. You will find all sorts of sources for updating your AMT La Frances. I agree that "policecarmodels.com" is a great resource. SSB Resins, Models by Dave, and Plaskit are also good places that I can personally recommend. Good luck with your project. Look forward to seeing your progress.
David