12v's used to be in a lot of trucks up here in the 70's, but the 92's lighter weight & more hp took over as far as the detroit powered trucks. the cats & cummins would get better fuel mileage & last longer between overhauls. Detroits are easy to get more hp out of but they don't live real long.
A contruction co. here has a fleet of Euclid B-70 off hiway belly dumps that were 12v71 powered, but they put 3406E cats in. the cat powered B-70's are a lot quieter, use less fuel, live longer,& will out pull the detroits
I haven't seen any old 12v powered trucks around here in about 10 years.
One redeeming factor factor that I can think of, is that I made alot of money working on 'em