The just sold an ambulance on ebay no rust, looked mint, 38,000 actual miles with an IDI diesel Best diesel Ford ever used according to this
https://autowise.com/ford-diesel-engine-history/ No computer to fail, dependable, easy & cheap to repair. Low milage are hard to find, but you have time. Get one from a fire dept not an ambulace service. Watch Bobs video
Mines a '93 & I couldn't be happier. This is a $250,000 build with more storage than I can use so I'll take some out. Maintain by law & fireman take care of their equipment. Mine is no rust will never leak, best build on the road, has legal seating for 6 & I paid $2000 with 80,000 actual miles. Let me know if I can help but I've never talked to any ambulance owner that wasn't as exited as I am about them. Good Luck!
D. Later is Better: If you have a choice, select the newest-model Ford IDI you can find, with the ’93 to ’94 years being best. You’ll get a better glow plug controller (D), serpentine belt system, and the turbo engine comes with stronger connecting rods. The 7.3L is desired more than the 6.9L because it has larger, ½-inch head bolts instead of 7⁄16-inch versions.