Those are so cool! What a find!
Back in the day, I had a Cox .049 Dune Buggy and several control line planes. I bought the Cox "Black Widow" .049 engine and then built a balsa control line model, ordered from the back of Model Airplane News, to put it in. It lasted about two spins before I piled it in. The little Black Widow lived on, though. I wish I knew where it was... I remember mounting it on a piece of lumber and demonstrating it at my buddy's repair shop. The guys were blown away by the screaming little monster.
I remember dreaming of the day I cold buy one of those big .40 engines and a remote control system! A four-channel R/C Tx/Rx and servos cost big bucks back then...