Didn't go with personalized plates on the ambulance, but DID score a set of 1966 Ohio plates at a swap meet last weekend. In Ohio if you have historical plates on your car you're allowed to run "year specific" plates if you can find a set.
For you Ohio guys who want to do this:
Buy a SET of plates (not just one) specific to the year of your car, take those plates with you to the DMV, they will make a photocopy of them for their records, then issue you a 2nd registration. You MUST keep at least 1 of you "historical vehicle" tags IN the car, but are allowed to then run the year-specific tags (Ohio used to issue new tags every year with that year's date stamped @ the bottom)
There were TWO added bonuses to this... Ohio 1966 plates are RED with WHITE letters (neat for a red & white ambo!) and you may be lucky enough to encounter Jim Tighe at the DMV like I did...