Just bought an st70 project

Hi, I race classic bikes and have been after a period type paddock bike that I can squeeze in the van.
Now managed to get an st70 project at a sensible price, but it was missing the engine.
A friend has donated a c50 engine, looking at the carb with no 90degree manifold is a very early one.
I believe the bike is a 1982 blue with silver stripe along the main frame and red dax sticker.
When did they change from 6v to 12v?
The bike loom has 4 wires in a connector plug
White
Yellow
Black and white
Red and green - neutral switch.

The engine loom has 5 wires
Red and green - neutral switch
Yellow
Green
Black
Pink

Is it possible to get it to run with this combination?