It's an old antique Zenoah conversion..41.5cc..Roush made stuff when quarter scale started...It's green on the back because it was probably a Green Machine brand industrial engine..
The bolt pattern on the front is the same still used for mounting the G45,62, and 80..The hex bolt on the bottom is the same as on the G38...
Ikeda still makes the G38 flywheels...
I can cross reference the carb if its a Walbro...