Flightcancled
The advantage to getting an ambulance and converting it later. Is that you can find the ambulance that you want. The already converted ones are not abundant so you pretty much get what you get.
My original plan was to convert mine to 4x4 with the ujoint kit. I wanted a srw mini-mod as the base but I kind of jumped the gun. I got impatient and got one with the idi motor.
It's a great motor, but after driving the powerstroke version I found I preferred it to the point that I did not want to put the money into converting the idi ambulance.
So I started to search for a powerstroke mini-mod. All the ones that I found had extremely high miles or were not mini-mods and had wide boxes (drw).
Eventually I came across a 4x4 cab and chassis with a powerstroke motor and low miles (It is the older less desirable 7.3 powerstroke). So far I am happy with it. It had a pretty bad fuel leak when I got it, but that us all taken care of now.
I hunted for a 4x4 ambulance for awhile. They are not easy to find.
There is one listed upstate ny but it is a bit pricey!!
If you are in a rush i would say your best bet would be to find a great 2wd ambulance with everything you want and convert it later. I guess it depends on how important 4wd is for you in the short term. Finding a really good 2wd 7.3 ambulance for a reasonable price is definitely possible.
Good luck with your search
Post pictures once you get something!!