Van to school bus conversions....when started?

QUESTION...  There are "short school buses" that you see around, common at retirement homes and private schools, that are conversions. That is, there is a shortened bus body that is mounted on a Econoline type van body (...front end, two doors, only...), usually extending over the cab, like a moving van. Hopefully the photo transitioned with this post. I am new here, and thought I would ask the experts out there.     When did these "short buses" first appear in this country.  I ask this because I am working with guys who want to use one in a 1960s historic program, and I want to make sure that the vehicle is accurate to the time.
   So, anyone know how long these have been around?
Thanks!

There were many Econoline/Falcon school busses in the 1960s, but they all retained the van shape.  The wider body conversions must have started in the 1970s or later.

The modified van / school bus like the one in your picture started in the mid 70s according to Wikipedia.

https://en.m.wikipedia.org/wiki/School_bus

Apparently the Busette started production in 1972.

http://www.statemaster.com/encyclopedia/Busette

Thank you, all!

All of us were glad to help?