The rear engine gas was used in school buses in the 60's. They were never very popular. Mechanics hated to work on them because of the lack of space. There were cooling problems with the engine and also heat problems inside the bus. Many were big V-6 engines that had their own issue. The crankshaft was not strong enough to handle the 400 cu. in power. This often caused block damage when the crank broke. The advantage in school bus was more space for entry and exit. They were also quiet. The concept is good, but no one spent the money to eliminate all of the problems.