Technical Voltage regulator for 12 Volt Generator 13 Amp Current Limit

The Ranger aircraft engines of WWII were used in many Hot Rods, Drag Cars and Sprint Cars in the 40's and 50's. They had had a direct driven generator that was totally enclosed, perhaps the reason for the 13 Amp rating. They used a typical 3 coil Delco Remy regulator, none of which I can find can be adjusted that low.

Any electrical or electronic gurus here have a thought about how to achieve this?

 

BTT