Oddly enough the 3 in the LA area never suffered a engine failure, which sounds ironic considering how LA has car chase after car chase nowadays. The other 9 would eventually have improvements made that would prevent further engine failures. (4 bolt main replacements)
(Apologies for the double post, I thought I was editing my previous post.)
I also came across this interesting chevy ambulance without the full lightbar. The rig next to it has an R to denote reserve status.
I also found some really good photos of the early Ford ambulances.