How many quarts of oil to fill a 1965 6 cylinder engine?

A 1965 6-cylinder engine's oil capacity isn't standardized; it varies significantly depending on the *make and model* of the car. There's no single answer.

To find the correct amount, you must consult your car's owner's manual. The manual will specify the exact oil capacity for your specific engine. Failing that, you can try looking up the specifications online using the make, model, and engine size (often found on a sticker under the hood).