Hard to tell from the photo's in one book I have , if the quarters are the same legnth. The Bonneville looks to have more sheet metal legnth ahead of the rear wheel than the Catalina. Contour lines appear to be the same on the 69 & 70. Some of the Cat's & Bons wore fender skirts.
If you only have one door on the driverside of the ambulance I'm guessing a quarter panel from a 2 door convert or hartop is way too short.
A friend has a 70 Caddy Hearse & he found out its like 20 inches longer than a Sedan Deville / Fleetwood Brougham. That extra legnth comes in in the quarter panel area, but the fender skirts are the same as the Coupe, Sedan & Fleetwood
I saw a beautiful 1964 Bonneville Ambulance for sale at a car show in
2002 for $9000 it had 60,000 miles on it.
Good Luck.
========= Harryface =========
1991 Pontiac Bonneville LE 3800 V6 ( C ), Black/Slate Grey _~_~_~287,124 miles_~_~_
~_~_~_~_U.S.A._~_~_~_~_~_
~~~The Former Fleet ~~~
89 Cavalier Z 24 convertible
78 Holiday 88 coupe
68 LeSabre convertible
73 Impala sedan