Here's why:
* Engine-Specific Information: Ignition point gaps vary depending on the specific engine model, year, and even the specific distributor used.
* Maintenance Manual: The most accurate information about the correct ignition point gap for your car will be in the original owner's manual or a reputable service manual for your 1939 Chevrolet Master Deluxe JA.
* Professional Assistance: If you can't find the information in a manual, it's best to consult a mechanic specializing in classic cars or a knowledgeable Chevrolet enthusiast. They can help you find the correct specification and ensure proper adjustment.
Important Note: Adjusting ignition point gaps requires technical knowledge and appropriate tools. Improper adjustment can harm your engine.