Rick,
A simple answer would be: Yes and No.
A more complex answer would be, Yes it can be done, but it would be seriously expensive. (You would pretty much need to pay someone to refabricate the entire rear end of the car.) The rear fenders and sheet metal on Ambulances was shipped to the coachbuilder seperate from the rest of the car. (In fact, the car was shipped as a hood, cowl, front fenders, and Bare frame. Everything from the windshield back was built by the coachbuilder.) While the fenders off of a “normal” ‘59 might look right, I think if you did some measuring you would start to notice differences in the lengths of the fender pieces, differences in the shape of the panel where it transitions into the car itself, and some other little differences. Also, the coachbuilders would make changes in the dies and the production process from year to year, so odds are that ’60 is a slightly different shape than a ‘59 anyways.
Looks can be decieving when it comes to parts that “Look” like they will fit.
Anything can be done if you throw enough money at it. My suggestion is if you like the ’60 and can afford it, just grab it and work with what you have. 99% of the public isnt going to know the difference. (I had an all white 1971 Cad Ambulance, and I had folks Yelling Ghostbusters at me all the time.) Pretty much any Cad ambulance can be converted and the public will be happy.
Will you be happy with a 1960 Ambulance? My personal feeling is if the car is solid and in fairly good condition, DONT cut it up. Paint and logos and equipment can make the car close enough for the public without killing the value of the car itself. ALL of these old Cadillac ambulances are getting rarer and harder to find. The more we cut up, the more that are lost forever. Also, if you ever want or need to sell it later, there is a REALLY small market for Ecto's to start with. And a car that's been seriously modified to make an Ecto is only worth something to that Ecto market. (And the folks with the money to buy a replica, are going to hold out for a ‘59 if they can anyways.) If you keep it as a ’60, then you could remove the “Ecto stuff” and open up the vintage ambulance collectors market if you did need to sell. My ‘59 Ecto-1a replica started out as a bare hulk ready for the crusher. The conversion saved this car. My ’59 ambulance is essentially intact, and I wouldnt even consider trying to convert it as the car itself is rare.
I collect Vintage ambulances and Hearses in addition to my Ecto, so I'm aware and active in that side of the hobby as well. I hate to see a perfectly good coach cut up. My suggestion is keep it stock and paint her up. Its cheaper for you in the long run, and better for the car as well.
TheEcto1a